U.S. patent number 8,736,256 [Application Number 13/205,209] was granted by the patent office on 2014-05-27 for rotating field sensor.
This patent grant is currently assigned to TDK Corporation. The grantee listed for this patent is Hiraku Hirabayashi, Yosuke Komasaki, Shunji Saruki. Invention is credited to Hiraku Hirabayashi, Yosuke Komasaki, Shunji Saruki.
United States Patent |
8,736,256 |
Komasaki , et al. |
May 27, 2014 |
Rotating field sensor
Abstract
A rotating field sensor includes a first detection circuit that
outputs a first signal indicating the intensity of a component of a
rotating magnetic field in a first direction, a second detection
circuit that outputs a second signal indicating the intensity of a
component of the rotating magnetic field in a second direction, and
an arithmetic circuit that calculates a detected angle value based
on the first and second signals. Each of the first and second
detection circuits includes at least one MR element row. Each MR
element row is composed of a plurality of MR elements connected in
series. Each MR element has a magnetization pinned layer. The
plurality of MR elements forming each MR element row include one or
more pairs of MR elements. Magnetization directions of the
magnetization pinned layers in two MR elements making up a pair
form a predetermined relative angle other than 0.degree. and
180.degree..
Inventors: |
Komasaki; Yosuke (Tokyo,
JP), Hirabayashi; Hiraku (Tokyo, JP),
Saruki; Shunji (Tokyo, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Komasaki; Yosuke
Hirabayashi; Hiraku
Saruki; Shunji |
Tokyo
Tokyo
Tokyo |
N/A
N/A
N/A |
JP
JP
JP |
|
|
Assignee: |
TDK Corporation (Tokyo,
JP)
|
Family
ID: |
44651221 |
Appl.
No.: |
13/205,209 |
Filed: |
August 8, 2011 |
Prior Publication Data
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|
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Document
Identifier |
Publication Date |
|
US 20120119729 A1 |
May 17, 2012 |
|
Foreign Application Priority Data
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|
|
|
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Nov 17, 2010 [JP] |
|
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2010-256380 |
|
Current U.S.
Class: |
324/207.21;
324/207.25 |
Current CPC
Class: |
G01R
33/093 (20130101); B82Y 25/00 (20130101); G01D
5/145 (20130101) |
Current International
Class: |
G01B
7/30 (20060101) |
Field of
Search: |
;324/207.13-207.21,244-263,207.25 ;365/157-158,170-173,225.5
;73/514.31,514.39,520.01,779,862.193,862.333 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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B2-2787783 |
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Aug 1998 |
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JP |
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B2-2990822 |
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Dec 1999 |
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JP |
|
A-2003-502674 |
|
Jan 2003 |
|
JP |
|
A-2003-502876 |
|
Jan 2003 |
|
JP |
|
A-2004-504713 |
|
Feb 2004 |
|
JP |
|
Primary Examiner: Vazquez; Arleen M
Assistant Examiner: Andrews; Brent J
Attorney, Agent or Firm: Oliff PLC
Claims
What is claimed is:
1. A rotating field sensor for detecting an angle that a direction
of a rotating magnetic field in a reference position forms with
respect to a reference direction, the rotating field sensor
comprising: a first detection circuit that detects an intensity of
a component of the rotating magnetic field in a first direction and
outputs a first signal indicating the intensity; a second detection
circuit that detects an intensity of a component of the rotating
magnetic field in a second direction and outputs a second signal
indicating the intensity; and an arithmetic circuit that
calculates, based on the first and second signals, a detected angle
value having a correspondence relationship with the angle that the
direction of the rotating magnetic field in the reference position
forms with respect to the reference direction, wherein: each of the
first and second detection circuits includes at least one row of
magnetoresistive elements; each of the at least one row of
magnetoresistive elements is composed of a plurality of
magnetoresistive elements connected in series; each of the
plurality of magnetoresistive elements has a magnetization pinned
layer whose magnetization direction is pinned, a free layer whose
magnetization direction varies according to the direction of the
rotating magnetic field, and a nonmagnetic layer disposed between
the magnetization pinned layer and the free layer; the number of
the plurality of magnetoresistive elements forming each row of
magnetoresistive elements is an even number not smaller than two;
the plurality of magnetoresistive elements forming each row of
magnetoresistive elements include one or more pairs of
magnetoresistive elements; the magnetization directions of the
magnetization pinned layers in two magnetoresistive elements making
up any of the one or more pairs form a predetermined relative angle
other than 0.degree. and 180.degree.; the at least one row of
magnetoresistive elements in the first detection circuit does not
include any magnetoresistive element that has a magnetization
pinned layer whose magnetization direction is pinned in the first
direction or in a direction opposite to the first direction; and
the at least one row of magnetoresistive elements in the second
detection circuit does not include any magnetoresistive element
that has a magnetization pinned layer whose magnetization direction
is pinned in the second direction or in a direction opposite to the
second direction.
2. The rotating field sensor according to claim 1, wherein the
second direction is orthogonal to the first direction.
3. The rotating field sensor according to claim 1, wherein each of
the first and second detection circuits includes, as the at least
one row of magnetoresistive elements, two rows of magnetoresistive
elements connected in series.
4. The rotating field sensor according to claim 1, wherein each of
the first and second detection circuits includes, as the at least
one row of magnetoresistive elements, first and second rows of
magnetoresistive elements connected in series and third and fourth
rows of magnetoresistive elements connected in series, the first to
fourth rows of magnetoresistive elements forming a Wheatstone
bridge circuit.
5. The rotating field sensor according to claim 4, wherein: the
magnetization pinned layer in each of the plurality of
magnetoresistive elements that form the third row of
magnetoresistive elements has the magnetization direction the same
as that of the magnetization pinned layer in a corresponding one of
the plurality of magnetoresistive elements that form the second row
of magnetoresistive elements; the magnetization pinned layer in
each of the plurality of magnetoresistive elements that form the
fourth row of magnetoresistive elements has the magnetization
direction the same as that of the magnetization pinned layer in a
corresponding one of the plurality of magnetoresistive elements
that form the first row of magnetoresistive elements; respective
corresponding ones of the magnetoresistive elements in the first
row and the fourth row whose magnetization pinned layers have the
same magnetization direction are disposed adjacent to each other;
and respective corresponding ones of the magnetoresistive elements
in the second row and the third row whose magnetization pinned
layers have the same magnetization direction are disposed adjacent
to each other.
6. The rotating field sensor according to claim 1, wherein: the
plurality of magnetoresistive elements that form the at least one
row of magnetoresistive elements in the first detection circuit
include only one pair of magnetoresistive elements, and the first
direction is an intermediate direction between the magnetization
directions of the magnetization pinned layers of two
magnetoresistive elements making up the pair, or is a direction
opposite to the intermediate direction; and the plurality of
magnetoresistive elements that form the at least one row of
magnetoresistive elements in the second detection circuit include
only one pair of magnetoresistive elements, and the second
direction is an intermediate direction between the magnetization
directions of the magnetization pinned layers of two
magnetoresistive elements making up the pair, or is a direction
opposite to the intermediate direction.
7. The rotating field sensor according to claim 1, wherein: the
plurality of magnetoresistive elements that form the at least one
row of magnetoresistive elements in the first detection circuit
include a first and a second pair of magnetoresistive elements; the
first direction is an intermediate direction between a third
direction and a fourth direction or is a direction opposite to the
intermediate direction, where the third direction is a direction
intermediate between the magnetization directions of the
magnetization pinned layers of two magnetoresistive elements making
up the first pair, and the fourth direction is a direction
intermediate between the magnetization directions of the
magnetization pinned layers of two magnetoresistive elements making
up the second pair; the plurality of magnetoresistive elements that
form the at least one row of magnetoresistive elements in the
second detection circuit include a third and a fourth pair of
magnetoresistive elements; and the second direction is an
intermediate direction between a fifth direction and a sixth
direction or is a direction opposite to the intermediate direction,
where the fifth direction is a direction intermediate between the
magnetization directions of the magnetization pinned layers of two
magnetoresistive elements making up the third pair, and the sixth
direction is a direction intermediate between the magnetization
directions of the magnetization pinned layers of two
magnetoresistive elements making up the fourth pair.
8. A rotating field sensor for detecting an angle that a direction
of a rotating magnetic field in a reference position forms with
respect to a reference direction, the rotating field sensor
comprising: a first detection circuit that detects an intensity of
a component of the rotating magnetic field in a first direction and
outputs a first signal indicating the intensity; a second detection
circuit that detects an intensity of a component of the rotating
magnetic field in a second direction and outputs a second signal
indicating the intensity; and an arithmetic circuit that
calculates, based on the first and second signals, a detected angle
value having a correspondence relationship with the angle that the
direction of the rotating magnetic field in the reference position
forms with respect to the reference direction, wherein: each of the
first and second detection circuits includes at least one row of
magnetoresistive elements; each of the at least one row of
magnetoresistive elements is composed of a plurality of
magnetoresistive elements connected in series along a potential
gradient that occurs when the first or second detection circuit is
in operation; each of the plurality of magnetoresistive elements
has a magnetization pinned layer whose magnetization direction is
pinned, a free layer whose magnetization direction varies according
to the direction of the rotating magnetic field, and a nonmagnetic
layer disposed between the magnetization pinned layer and the free
layer; the number of the plurality of magnetoresistive elements
forming each row of magnetoresistive elements is an even number not
smaller than two; the plurality of magnetoresistive elements
forming each row of magnetoresistive elements include one or more
pairs of magnetoresistive elements; the magnetization directions of
the magnetization pinned layers in two magnetoresistive elements
making up any of the one or more pairs form a predetermined
relative angle other than 0.degree. and 180.degree.; the at least
one row of magnetoresistive elements in the first detection circuit
does not include any magnetoresistive element that has a
magnetization pinned layer whose magnetization direction is pinned
in the first direction or in a direction opposite to the first
direction; and the at least one row of magnetoresistive elements in
the second detection circuit does not include any magnetoresistive
element that has a magnetization pinned layer whose magnetization
direction is pinned in the second direction or in a direction
opposite to the second direction.
9. A rotating field sensor for detecting an angle that a direction
of a rotating magnetic field in a reference position forms with
respect to a reference direction, the rotating field sensor
comprising: a first detection circuit that detects an intensity of
a component of the rotating magnetic field in a first direction and
outputs a first signal indicating the intensity; a second detection
circuit that detects an intensity of a component of the rotating
magnetic field in a second direction and outputs a second signal
indicating the intensity; and an arithmetic circuit that
calculates, based on the first and second signals, a detected angle
value having a correspondence relationship with the angle that the
direction of the rotating magnetic field in the reference position
forms with respect to the reference direction, wherein: each of the
first and second detection circuits includes at least one row of
magnetoresistive elements, and a power supply port receiving a
predetermined voltage; each of the at least one row of
magnetoresistive elements is composed of a plurality of
magnetoresistive elements connected in series when viewed from the
power supply port; each of the plurality of magnetoresistive
elements has a magnetization pinned layer whose magnetization
direction is pinned, a free layer whose magnetization direction
varies according to the direction of the rotating magnetic field,
and a nonmagnetic layer disposed between the magnetization pinned
layer and the free layer; the number of the plurality of
magnetoresistive elements forming each row of magnetoresistive
elements is an even number not smaller than two; the plurality of
magnetoresistive elements forming each row of magnetoresistive
elements include one or more pairs of magnetoresistive elements;
the magnetization directions of the magnetization pinned layers in
two magnetoresistive elements making up any of the one or more
pairs form a predetermined relative angle other than 0.degree. and
180.degree.; the at least one row of magnetoresistive elements in
the first detection circuit does not include any magnetoresistive
element that has a magnetization pinned layer whose magnetization
direction is pinned in the first direction or in a direction
opposite to the first direction; and the at least one row of
magnetoresistive elements in the second detection circuit does not
include any magnetoresistive element that has a magnetization
pinned layer whose magnetization direction is pinned in the second
direction or in a direction opposite to the second direction.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rotating field sensor for
detecting an angle that the direction of a rotating magnetic field
forms with respect to a reference direction.
2. Description of the Related Art
In recent years, rotating field sensors have been widely used to
detect the rotational position of an object in various applications
such as detecting the rotational position of an automotive steering
wheel. Rotating field sensors are used not only to detect the
rotational position of an object but also to detect a linear
displacement of an object. Systems using rotating field sensors are
typically provided with means (for example, a magnet) for
generating a rotating magnetic field whose direction rotates in
conjunction with the rotation or linear movement of the object. The
rotating field sensors use magnetic detection elements to detect
the angle that the direction of the rotating magnetic field forms
with respect to a reference direction. The rotational position or
linear displacement of the object is thus detected.
There has been known a rotating field sensor that has two bridge
circuits (Wheatstone bridge circuits) as shown in U.S. Pat. No.
6,633,462 B2, U.S. Pat. No. 5,363,034, U.S. Pat. No. 5,216,363,
U.S. Pat. No. 6,465,053 B1, and U.S. Pat. No. 6,501,678 B1. In such
a rotating field sensor, each of the two bridge circuits includes
four magnetoresistive elements (hereinafter, also referred to as MR
elements) serving as magnetic detection elements. Each of the
bridge circuits detects the intensity of a component of the
rotating magnetic field in one direction, and outputs a signal that
indicates the intensity. The output signals of the two bridge
circuits differ in phase by 1/4 the period of the output signals of
the bridge circuits. The angle that the direction of the rotating
magnetic field forms with respect to a reference direction is
calculated based on the output signals of the two bridge
circuits.
In a rotating field sensor that uses an MR element as a magnetic
detection element, the waveform of the output signal of the MR
element corresponding to the resistance ideally traces a sinusoidal
curve (including a sine waveform and a cosine waveform) as the
direction of the rotating magnetic field rotates. However, it is
known that the output signal waveform of an MR element can be
distorted from a sinusoidal curve, as described in U.S. Pat. No.
6,633,462 B2. Distortion of the output signal waveform of an MR
element from a sinusoidal curve means that the output signal of the
MR element includes a harmonic component other than a fundamental
sinusoidal component, as described in U.S. Pat. Nos. 5,363,034 and
5,216,363. The harmonic component included in the output signal of
the MR element may cause an error in the angle detected by the
rotating field sensor. The error is mainly caused by a second and a
third harmonic component.
U.S. Pat. No. 6,633,462 B2 discloses a magnetoresistive sensor
including a main sensing element having a main reference
magnetization axis, and two correction sensing elements having
their respective reference magnetization axes inclined with respect
to the main reference magnetization axis. The two correction
sensing elements are electrically connected to the main sensing
element to correct the detected angle. The two correction sensing
elements output signals that are out of phase with each other by a
half period of an error signal of the main sensing element. In this
sensor, the output signals of the two correction sensing elements
are added to the output signal of the main sensing element. This
allows for eliminating at least part of the error signal of the
main sensing element. The sensor disclosed in U.S. Pat. No.
6,633,462 B2, however, has a drawback of increasing in size because
the two correction sensing elements are required in addition to the
main sensing element. Further, the sensor requires that the
resistances of the correction sensing elements be set to an optimum
value different from that of the main sensing element. This poses a
problem that it is not easy to design and manufacture this
sensor.
U.S. Pat. Nos. 5,363,034 and 5,216,363 disclose a technique for
reducing harmonic components of the output signal of a magnetic
sensor that is disposed to face a magnetic scale in which magnets
are arrayed with a predetermined pitch. According to the technique,
the harmonic components are reduced by serially connecting a
plurality of magnetoresistive elements that are spaced apart from
each other by a predetermined distance in the direction in which
the magnets are arrayed. However, this technique requires that the
arrangement of the plurality of magnetoresistive elements be
changed according to the array pitch of the magnets because the
arrangement of the magnetoresistive elements depends on the array
pitch of the magnets. For this reason, this technique has the
problem that it cannot be applied to the case where the magnets are
arrayed with an arbitrary pitch.
OBJECT AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a rotating
field sensor for detecting an angle that the direction of a
rotating magnetic field forms with respect to a reference
direction, the rotating field sensor being capable of reducing
errors in the detected angle with a simple configuration.
A rotating field sensor of the present invention detects an angle
that the direction of a rotating magnetic field in a reference
position forms with respect to a reference direction. The rotating
field sensor includes a first detection circuit, a second detection
circuit, and an arithmetic circuit. The first detection circuit
detects the intensity of a component of the rotating magnetic field
in a first direction and outputs a first signal indicating the
intensity. The second detection circuit detects the intensity of a
component of the rotating magnetic field in a second direction and
outputs a second signal indicating the intensity. The arithmetic
circuit calculates, based on the first and second signals, a
detected angle value having a correspondence relationship with the
angle that the direction of the rotating magnetic field in the
reference position forms with respect to the reference
direction.
Each of the first and second detection circuits includes at least
one row of magnetoresistive elements. Each row of magnetoresistive
elements is composed of a plurality of magnetoresistive elements
connected in series. Each of the plurality of magnetoresistive
elements has a magnetization pinned layer whose magnetization
direction is pinned, a free layer whose magnetization direction
varies according to the direction of the rotating magnetic field,
and a nonmagnetic layer disposed between the magnetization pinned
layer and the free layer. The number of the plurality of
magnetoresistive elements forming each row of magnetoresistive
elements is an even number not smaller than two.
The plurality of magnetoresistive elements forming each row of
magnetoresistive elements include one or more pairs of
magnetoresistive elements. The magnetization directions of the
magnetization pinned layers in two magnetoresistive elements making
up a pair form a predetermined relative angle other than 0.degree.
and 180.degree..
The at least one row of magnetoresistive elements in the first
detection circuit does not include any magnetoresistive element
that has a magnetization pinned layer whose magnetization direction
is pinned in the first direction or in a direction opposite to the
first direction. The at least one row of magnetoresistive elements
in the second detection circuit does not include any
magnetoresistive element that has a magnetization pinned layer
whose magnetization direction is pinned in the second direction or
in a direction opposite to the second direction.
In the rotating field sensor of the present invention, the
potential difference across each magnetoresistive element
corresponding to the resistance of the magnetoresistive element
varies periodically as the direction of the rotating magnetic field
rotates. The periodically varying component of the potential
difference across each magnetoresistive element may include a
harmonic component in addition to an ideal sinusoidal component. As
used herein, the term "harmonic component" with no order specified
shall include not only a harmonic component of a single order but
also a combination of harmonic components of multiple orders. The
harmonic component may cause some error in the angle detected by
the rotating field sensor. In the rotating field sensor of the
present invention, the magnetization directions of the
magnetization pinned layers in two magnetoresistive elements making
up a pair form a predetermined relative angle other than 0.degree.
and 180.degree.. For this reason, the harmonic component produced
in the potential difference across one magnetoresistive element of
a pair of magnetoresistive elements and the harmonic component
produced in the potential difference across the other
magnetoresistive element of the pair are out of phase with each
other. Furthermore, in the present invention, two magnetoresistive
elements making up a pair are connected in series. This allows the
harmonic component produced in the potential difference across one
magnetoresistive element of a pair of magnetoresistive elements and
the harmonic component produced in the potential difference across
the other magnetoresistive element of the pair to be combined with
each other, thereby allowing a reduction in the harmonic component
in the potential difference across the pair of magnetoresistive
elements. As a result, it is possible to reduce the error in the
angle detected by the rotating field sensor.
In the rotating field sensor of the present invention, the second
direction may be orthogonal to the first direction. Each of the
first and second detection circuits may include, as the at least
one row of magnetoresistive elements, two rows of magnetoresistive
elements connected in series. Alternatively, each of the first and
second detection circuits may include, as the at least one row of
magnetoresistive elements, first and second rows of
magnetoresistive elements connected in series and third and fourth
rows of magnetoresistive elements connected in series. The first to
fourth rows of magnetoresistive elements may form a Wheatstone
bridge circuit.
Where the first to fourth rows of magnetoresistive elements form a
Wheatstone bridge circuit, the magnetization pinned layer in each
of the plurality of magnetoresistive elements that form the third
row of magnetoresistive elements may have the magnetization
direction the same as that of the magnetization pinned layer in a
corresponding one of the plurality of magnetoresistive elements
that form the second row of magnetoresistive elements, and the
magnetization pinned layer in each of the plurality of
magnetoresistive elements that form the fourth row of
magnetoresistive elements may have the magnetization direction the
same as that of the magnetization pinned layer in a corresponding
one of the plurality of magnetoresistive elements that form the
first row of magnetoresistive elements. In this case, respective
corresponding ones of the magnetoresistive elements in the first
row and the fourth row whose magnetization pinned layers have the
same magnetization direction may be disposed adjacent to each
other, while respective corresponding ones of the magnetoresistive
elements in the second row and the third row whose magnetization
pinned layers have the same magnetization direction may be disposed
adjacent to each other.
In the rotating field sensor of the present invention, the
plurality of magnetoresistive elements that form the at least one
row of magnetoresistive elements in the first detection circuit may
include only one pair of magnetoresistive elements. In this case,
the first direction may be an intermediate direction between the
magnetization directions of the magnetization pinned layers of two
magnetoresistive elements making up the pair, or may be a direction
opposite to the intermediate direction. The plurality of
magnetoresistive elements that form the at least one row of
magnetoresistive elements in the second detection circuit may
include only one pair of magnetoresistive elements. In this case,
the second direction may be an intermediate direction between the
magnetization directions of the magnetization pinned layers of two
magnetoresistive elements making up the pair, or may be a direction
opposite to the intermediate direction.
In the rotating field sensor of the present invention, the
plurality of magnetoresistive elements that form the at least one
row of magnetoresistive elements in the first detection circuit may
include a first and a second pair of magnetoresistive elements. In
this case, the first direction may be an intermediate direction
between a third direction and a fourth direction or may be a
direction opposite to the intermediate direction, where the third
direction is a direction intermediate between the magnetization
directions of the magnetization pinned layers of two
magnetoresistive elements making up the first pair, and the fourth
direction is a direction intermediate between the magnetization
directions of the magnetization pinned layers of two
magnetoresistive elements making up the second pair. The plurality
of magnetoresistive elements that form the at least one row of
magnetoresistive elements in the second detection circuit may
include a third and a fourth pair of magnetoresistive elements. In
this case, the second direction may be an intermediate direction
between a fifth direction and a sixth direction or may be a
direction opposite to the intermediate direction, where the fifth
direction is a direction intermediate between the magnetization
directions of the magnetization pinned layers of two
magnetoresistive elements making up the third pair, and the sixth
direction is a direction intermediate between the magnetization
directions of the magnetization pinned layers of two
magnetoresistive elements making up the fourth pair.
As described above, the rotating field sensor of the present
invention makes it possible to reduce the harmonic component in the
potential difference across a pair of magnetoresistive elements.
This allows reducing the error in the angle detected by the
rotating field sensor. Furthermore, in the rotating field sensor of
the present invention, the at least one row of magnetoresistive
elements in the first detection circuit does not include any
magnetoresistive element that has a magnetization pinned layer
whose magnetization direction is pinned in the first direction or
in the direction opposite to the first direction, and the at least
one row of magnetoresistive elements in the second detection
circuit does not include any magnetoresistive element that has a
magnetization pinned layer whose magnetization direction is pinned
in the second direction or in the direction opposite to the second
direction. This makes it possible to reduce the number of
magnetoresistive elements to be included in each detection circuit
and makes it easier to design each detection circuit, as compared
with a case where the first detection circuit includes a
magnetoresistive element that has a magnetization pinned layer
whose magnetization direction is pinned in the first direction or
in the direction opposite to the first direction while the second
detection circuit includes a magnetoresistive element that has a
magnetization pinned layer whose magnetization direction is pinned
in the second direction or in the direction opposite to the second
direction. Consequently, according to the present invention, it is
possible to reduce the error in the detected angle with a simple
configuration.
Other and further objects, features and advantages of the present
invention will appear more fully from the following
description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view showing the general configuration of a
rotating field sensor according to a first embodiment of the
invention.
FIG. 2 is an explanatory diagram illustrating the definitions of
directions and angles in the first embodiment of the invention.
FIG. 3 is a circuit diagram showing the configuration of the
rotating field sensor according to the first embodiment of the
invention.
FIG. 4 is an explanatory diagram illustrating the magnetization
directions of magnetization pinned layers in a pair of MR elements
that form an MR element row in the rotating field sensor shown in
FIG. 3.
FIG. 5A and FIG. 5B are plan views of two units that respectively
incorporate the two bridge circuits of the rotating field sensor
shown in FIG. 3.
FIG. 6 is a plan view showing a plurality of lower electrodes that
are provided in a section shown in FIG. 5A and FIG. 5B.
FIG. 7 is a perspective view showing a part of an MR element of
FIG. 5A and FIG. 5B.
FIG. 8 is a waveform chart showing an example of the waveform of a
periodically varying component of the potential difference across
each of two MR elements making up a pair in the first embodiment of
the invention.
FIG. 9 is a waveform chart showing an example of the waveform of a
periodically varying component of the potential difference across
each of two MR elements making up another pair in the first
embodiment of the invention.
FIG. 10 is a waveform chart showing the waveform of a periodically
varying component of the potential difference across a pair of MR
elements in the first embodiment of the invention.
FIG. 11 is an explanatory diagram showing the angle at which the
resistance harmonic component of an MR element row determined by a
first simulation becomes minimum in magnitude.
FIG. 12 is an explanatory diagram showing an angular error of a
rotating field sensor of a comparative example determined by a
second simulation.
FIG. 13 is an explanatory diagram showing an angular error of the
rotating field sensor according to the first embodiment of the
invention determined by the second simulation.
FIG. 14 is a characteristic chart illustrating an example of the
relationship between the angular error and the relative angle that
is formed by the magnetization directions of the magnetization
pinned layers in two MR elements making up a pair in the first
embodiment of the invention.
FIG. 15 is a waveform chart showing the waveform of the angular
error of the rotating field sensor of the comparative example.
FIG. 16 is a waveform chart showing the waveform of the angular
error that results when a relative angle of 46.degree. is formed by
the magnetization directions of the magnetization pinned layers in
two MR elements making up a pair in the first embodiment of the
invention.
FIG. 17 is an explanatory diagram showing the configuration of a
rotating field sensor of a first modification example of the first
embodiment of the invention.
FIG. 18 is an explanatory diagram showing the configuration of a
rotating field sensor of a second modification example of the first
embodiment of the invention.
FIG. 19 is a plan view of a unit that incorporates four bridge
circuits of a rotating field sensor according to a second
embodiment of the invention.
FIG. 20 is a circuit diagram showing the configuration of a
rotating field sensor according to a third embodiment of the
invention.
FIG. 21 is an explanatory diagram illustrating the magnetization
directions of the magnetization pinned layers in a first and a
second pair of MR elements that form an MR element row in the
rotating field sensor shown in FIG. 20.
FIG. 22 is an explanatory diagram illustrating the relationship
between the angles of first to third types in the first detection
circuit of the third embodiment of the invention.
FIG. 23 is an explanatory diagram illustrating the relationship
between the angles of first to third types in the second detection
circuit of the third embodiment of the invention.
FIG. 24 is a plan view of a unit that incorporates the four bridge
circuits of the rotating field sensor according to the third
embodiment of the invention.
FIG. 25 is a waveform chart showing the waveform of a periodically
varying component of the potential difference across a first
virtual MR element.
FIG. 26 is a waveform chart showing the waveform of a periodically
varying component of the potential difference across a second
virtual MR element.
FIG. 27 is a waveform chart showing the waveform of a periodically
varying component of the potential difference across a third
virtual MR element.
FIG. 28 is a waveform chart showing the waveform of a periodically
varying component of the potential difference between a first end
and a second end of a virtual MR element row.
FIG. 29 is a waveform chart showing the waveform of a periodically
varying component of the potential difference across one of two MR
elements making up a first pair in the third embodiment of the
invention.
FIG. 30 is a waveform chart showing the waveform of a periodically
varying component of the potential difference across the other of
the two MR elements making up the first pair in the third
embodiment of the invention.
FIG. 31 is a waveform chart showing the waveform of a periodically
varying component of the potential difference across one of two MR
elements making up a second pair in the third embodiment of the
invention.
FIG. 32 is a waveform chart showing the waveform of a periodically
varying component of the potential difference across the other of
the two MR elements making up the second pair in the third
embodiment of the invention.
FIG. 33 is a waveform chart showing the waveform of a periodically
varying component of the potential difference between a first end
and a second end of an MR element row of the third embodiment of
the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
Preferred embodiments of the present invention will now be
described in detail with reference to the drawings. First,
reference is made to FIG. 1 and FIG. 2 to describe the general
configuration of a rotating field sensor according to a first
embodiment of the invention. FIG. 1 is a perspective view showing
the general configuration of the rotating field sensor according to
the present embodiment. FIG. 2 is an explanatory diagram
illustrating the definitions of directions and angles in the
present embodiment.
As shown in FIG. 1, the rotating field sensor 1 according to the
present embodiment detects the angle that the direction of a
rotating magnetic field MF in a reference position forms with
respect to a reference direction. In FIG. 1, a cylindrical magnet 2
is shown as an example of means for generating the rotating
magnetic field MF whose direction rotates. The magnet 2 has an N
pole and an S pole that are arranged symmetrically with respect to
a virtual plane including the central axis of the cylinder. The
magnet 2 rotates about the central axis of the cylinder.
Consequently, the direction of the rotating magnetic field MF
generated by the magnet 2 rotates about a center of rotation C
including the central axis of the cylinder. The rotating field
sensor 1 is disposed to face one end face of the magnet 2. The
means for generating the rotating magnetic field MF whose direction
rotates is not limited to the magnet 2 shown in FIG. 1, as will be
described later in relation to a modification example of the
present embodiment.
With reference to FIG. 2, the definitions of directions and angles
in the present embodiment will be described. First, a direction
that is parallel to the center of rotation C shown in FIG. 1 and is
from the one end face of the magnet 2 to the rotating field sensor
1 will be defined as the Z direction. Next, two mutually-orthogonal
directions on a virtual plane perpendicular to the Z direction will
be defined as the X direction and Y direction. In FIG. 2, the X
direction is shown as the direction toward the right, and the Y
direction is shown as the upward direction. The direction opposite
to the X direction will be defined as the -X direction, and the
direction opposite to the Y direction will be defined as the -Y
direction.
The reference position PR is the position where the rotating field
sensor 1 detects the rotating magnetic field MF. For example, the
reference position PR shall be where the rotating field sensor 1 is
located. The reference direction DR shall be the Y direction. The
angle that the direction DM of the rotating magnetic field MF in
the reference position PR forms with respect to the reference
direction DR will be designated by symbol .theta.. The direction DM
of the rotating magnetic field MF shall rotate clockwise in FIG. 2.
The angle .theta. will be expressed in a positive value when seen
clockwise from the reference direction DR, and in a negative value
when seen counterclockwise from the reference direction DR.
The rotating field sensor 1 detects, in the reference position PR,
a component of the rotating magnetic field MF in a first direction
D1 and a component of the rotating magnetic field MF in a second
direction D2. In the present embodiment, the second direction D2 is
orthogonal to the first direction D1, and coincides with the
reference direction DR (the Y direction). The first direction D1 is
the direction rotated from the second direction D2 (the reference
direction DR) by 90.degree..
Next, the configuration of the rotating field sensor 1 will be
described in detail with reference to FIG. 3. FIG. 3 is a circuit
diagram showing the configuration of the rotating field sensor 1.
The rotating field sensor 1 includes a first detection circuit 11,
a second detection circuit 12, and an arithmetic circuit 13. The
first detection circuit 11 detects the intensity of the component
of the rotating magnetic field MF in the first direction D1 and
outputs a first signal S1 indicating the intensity. The second
detection circuit 12 detects the intensity of the component of the
rotating magnetic field MF in the second direction D2 and outputs a
second signal S2 indicating the intensity. The arithmetic circuit
13 calculates, based on the first signal S1 and the second signal
S2, a detected angle value .theta.s having a correspondence
relationship with the angle .theta. that the direction DM of the
rotating magnetic field MF in the reference position PR forms with
respect to the reference direction DR. The arithmetic circuit 13
can be implemented by a single microcomputer, for example. The
method of calculating the detected angle value .theta.s will be
described in detail later.
The first signal S1 and the second signal S2 vary periodically with
the same signal period T. In the present embodiment, the second
signal S2 preferably differs from the first signal S1 in phase by
an odd number of times 1/4 the signal period T. However, in
consideration of the production accuracy of the magnetic detection
elements and other factors, the difference in phase between the
first signal S1 and the second signal S2 can be slightly different
from an odd number of times 1/4 the signal period T. The following
description assumes that the phases of the first signal S1 and the
second signal S2 satisfy the aforementioned preferable
relationship.
Each of the first and second detection circuits 11 and 12 includes
at least one row of magnetoresistive (MR) elements (hereinafter
referred to as MR element row). Each MR element row is composed of
a plurality of MR elements connected in series. As will be
described in detail later, each MR element has a magnetization
pinned layer whose magnetization direction is pinned, a free layer
whose magnetization direction varies according to the direction of
the rotating magnetic field, and a nonmagnetic layer disposed
between the magnetization pinned layer and the free layer. The
number of the plurality of MR elements forming each MR element row
is an even number not smaller than two. The plurality of MR
elements forming each MR element row include one or more pairs of
MR elements. The magnetization directions of the magnetization
pinned layers in two MR elements making up a pair form a
predetermined relative angle other than 0.degree. and
180.degree..
Each of the first and second detection circuits 11 and 12 may
include, as the at least one MR element row, two MR element rows
connected in series. Alternatively, each of the first and second
detection circuits 11 and 12 may include, as the at least one MR
element row, first and second MR element rows connected in series
and third and fourth MR element rows connected in series. The first
to fourth MR element rows may form a Wheatstone bridge circuit. The
following description will deal with the case where the first to
fourth MR element rows form a Wheatstone bridge circuit.
The first detection circuit 11 has a Wheatstone bridge circuit 14
and a difference detector 15. The Wheatstone bridge circuit 14
includes a power supply port V1, a ground port G1, two output ports
E11 and E12, first and second MR element rows R11 and R12 connected
in series, and third and fourth MR element rows R13 and R14
connected in series. Each of the first to fourth MR element rows
R11 to R14 is composed of a plurality of MR elements connected in
series. Each of the first to fourth MR element rows R11 to R14 has
a first end and a second end.
The first end of the first MR element row R11 and the first end of
the third MR element row R13 are connected to the power supply port
V1. The second end of the first MR element row R11 is connected to
the first end of the second MR element row R12 and the output port
E11. The second end of the third MR element row R13 is connected to
the first end of the fourth MR element row R14 and the output port
E12. The second end of the second MR element row R12 and the second
end of the fourth MR element row R14 are connected to the ground
port G1. A power supply voltage of predetermined magnitude is
applied to the power supply port V1. The ground port G1 is
grounded. The difference detector 15 outputs to the arithmetic
circuit 13 a signal corresponding to the potential difference
between the output ports E11 and E12 as the first signal S1.
The second detection circuit 12 has a Wheatstone bridge circuit 16
and a difference detector 17. The Wheatstone bridge circuit 16
includes a power supply port V2, a ground port G2, two output ports
E21 and E22, first and second MR element rows R21 and R22 connected
in series, and third and fourth MR element rows R23 and R24
connected in series. Each of the first to fourth MR element rows
R21 to R24 is composed of a plurality of MR elements connected in
series. Each of the first to fourth MR element rows R21 to R24 has
a first end and a second end.
The first end of the first MR element row R21 and the first end of
the third MR element row R23 are connected to the power supply port
V2. The second end of the first MR element row R21 is connected to
the first end of the second MR element row R22 and the output port
E21. The second end of the third MR element row R23 is connected to
the first end of the fourth MR element row R24 and the output port
E22. The second end of the second MR element row R22 and the second
end of the fourth MR element row R24 are connected to the ground
port G2. A power supply voltage of predetermined magnitude is
applied to the power supply port V2. The ground port G2 is
grounded. The difference detector 17 outputs to the arithmetic
circuit 13 a signal corresponding to the potential difference
between the output ports E21 and E22 as the second signal S2.
In the present embodiment, all the MR elements included in the
Wheatstone bridge circuits (hereinafter, referred to as bridge
circuits) 14 and 16 are TMR elements. However, GMR elements may be
employed instead of the TMR elements. The TMR elements or GMR
elements each have a magnetization pinned layer whose magnetization
direction is pinned, a free layer whose magnetization direction
varies according to the direction of the rotating magnetic field
MF, and a nonmagnetic layer disposed between the magnetization
pinned layer and the free layer. For TMR elements, the nonmagnetic
layer is a tunnel barrier layer. For GMR elements, the nonmagnetic
layer is a nonmagnetic conductive layer. The TMR elements or GMR
elements vary in resistance depending on the angle that the
magnetization direction of the free layer forms with respect to the
magnetization direction of the magnetization pinned layer. The
resistance reaches its minimum value when the foregoing angle is
0.degree.. The resistance reaches its maximum value when the
foregoing angle is 180.degree.. In FIG. 3, the filled arrows
indicate the magnetization directions of the magnetization pinned
layers in the MR elements. The hollow arrows indicate the
magnetization directions of the free layers in the MR elements.
In the first detection circuit 11, the magnetization directions of
the magnetization pinned layers in the plurality of MR elements are
pinned so that the potential difference between the output ports
E11 and E12 varies according to the intensity of the component of
the rotating magnetic field MF in the first direction D1. The first
direction D1 therefore serves as a reference direction when the
first detection circuit 11 detects the rotating magnetic field MF.
The first detection circuit 11 detects the intensity of the
component of the rotating magnetic field MF in the first direction
D1, and outputs the first signal. S1 indicating the intensity. In
the example shown in FIG. 3, the magnetization directions of the
magnetization pinned layers in the plurality of MR elements are
pinned so that the potential difference between the output ports
E11 and E12 varies according to the intensity of the component of
the rotating magnetic field MF in the X direction. In this example,
the first direction D1 is the same as the X direction.
In the second detection circuit 12, the magnetization directions of
the magnetization pinned layers in the plurality of MR elements are
pinned so that the potential difference between the output ports
E21 and E22 varies according to the intensity of the component of
the rotating magnetic field MF in the second direction D2. The
second direction D2 therefore serves as a reference direction when
the second detection circuit 12 detects the rotating magnetic field
MF. The second detection circuit 12 detects the intensity of the
component of the rotating magnetic field MF in the second direction
D2, and outputs the second signal S2 indicating the intensity. In
the example shown in FIG. 3, the magnetization directions of the
magnetization pinned layers in the plurality of MR elements are
pinned so that the potential difference between the output ports
E21 and E22 varies according to the intensity of the component of
the rotating magnetic field MF in the Y direction. In this example,
the second direction D2 is the same as the Y direction.
Now, a detailed description will be given of a plurality of MR
elements that form each MR element row. First, a plurality of MR
elements forming the first to fourth MR element rows R11, R12, R13,
and R14 of the bridge circuit 14 will be described. Each of the
first to fourth MR element rows R11, R12, R13, and R14 is composed
of two MR elements connected in series. The first MR element row
R11 is composed of a pair of MR elements R111 and R112. The second
MR element row R12 is composed of a pair of MR elements R121 and
R122. The third MR element row R13 is composed of a pair of MR
elements R131 and R132. The fourth MR element row R14 is composed
of a pair of MR elements R141 and R142.
One end of the MR element R111 serves as the first end of the first
MR element row R11. The other end of the MR element R111 is
connected to one end of the MR element R112. The other end of the
MR element R112 serves as the second end of the first MR element
row R11.
One end of the MR element R121 serves as the first end of the
second MR element row R12. The other end of the MR element R121 is
connected to one end of the MR element R122. The other end of the
MR element R122 serves as the second end of the second MR element
row R12.
One end of the MR element R131 serves as the first end of the third
MR element row R13. The other end of the MR element R131 is
connected to one end of the MR element R132. The other end of the
MR element R132 serves as the second end of the third MR element
row R13.
One end of the MR element R141 serves as the first end of the
fourth MR element row R14. The other end of the MR element R141 is
connected to one end of the MR element R142. The other end of the
MR element R142 serves as the second end of the fourth MR element
row R14.
Note that the MR elements R111 and R112 forming the first MR
element row R11 have only to be connected in series between the
first and second ends of the first MR element row R11, and may be
arranged in the order opposite to that in the example shown in FIG.
3. Likewise, two MR elements forming each of the other MR element
rows have only to be connected in series between the first and
second ends of the MR element row, and may be arranged in the order
opposite to that in the example shown in FIG. 3.
Now, a description will be given of the magnetization directions of
the magnetization pinned layers in the MR elements R111, R112,
R121, R122, R131, R132, R141, and R142. FIG. 4 is an explanatory
diagram showing the magnetization directions of the magnetization
pinned layers in the pair of MR elements R111 and R112 forming the
first MR element row R11. In FIG. 4, the arrows with symbols D111
and D112 indicate the magnetization directions of the magnetization
pinned layers in the MR elements R111 and R112, respectively. The
magnetization directions D111 and D112 of the magnetization pinned
layers in the MR elements R111 and R112 are pinned so that the
intermediate direction between the directions D111 and D112 is the
same as the first direction D1 (the X direction). The magnetization
directions D111 and D112 of the magnetization pinned layers in the
MR elements R111 and R112 form a predetermined relative angle
2.phi. other than 0.degree. and 180.degree.. The magnetization
direction D111 of the magnetization pinned layer in the MR element
R111 is the direction rotated clockwise from the first direction D1
by an angle .phi.. The magnetization direction D112 of the
magnetization pinned layer in the MR element R112 is the direction
rotated counterclockwise from the first direction D1 by the angle
.phi..
The magnetization directions of the magnetization pinned layers in
the pair of MR elements R121 and R122 forming the second MR element
row R12 are pinned so that the intermediate direction between those
magnetization directions is opposite to the first direction D1,
i.e., the -X direction. The magnetization directions of the
magnetization pinned layers in the pair of MR elements R131 and
R132 forming the third MR element row R13 are also pinned so that
the intermediate direction between those magnetization directions
is opposite to the first direction D1. The magnetization direction
of the magnetization pinned layer in the MR element R131 is the
same as that of the magnetization pinned layer in the MR element
R121. The magnetization direction of the magnetization pinned layer
in the MR element R132 is the same as that of the magnetization
pinned layer in the MR element R122. The magnetization direction of
the magnetization pinned layers in the MR elements R121 and R131 is
opposite to the magnetization direction D111 of the magnetization
pinned layer in the MR element R111 shown in FIG. 4. The
magnetization direction of the magnetization pinned layers in the
MR elements R122 and R132 is opposite to the magnetization
direction D112 of the magnetization pinned layer in the MR element
R112 shown in FIG. 4.
The magnetization directions of the magnetization pinned layers in
the MR elements R121 and R122 form a relative angle 2.phi.. The
magnetization directions of the magnetization pinned layers in the
MR elements R131 and R132 also form the relative angle 2.phi.. The
magnetization direction of the magnetization pinned layers in the
MR elements R121 and R131 is the direction rotated clockwise by the
angle .phi. from the direction opposite to the first direction D1.
The magnetization direction of the magnetization pinned layers in
the MR elements R122 and R132 is the direction rotated
counterclockwise by the angle .phi. from the direction opposite to
the first direction D1.
The magnetization directions of the magnetization pinned layers in
the pair of MR elements R141 and R142 forming the fourth MR element
row R14 are pinned so that the intermediate direction between those
magnetization directions is the same as the first direction D1 (the
X direction). The magnetization direction of the magnetization
pinned layer in the MR element R141 is the same as the
magnetization direction D111 of the magnetization pinned layer in
the MR element R111 shown in FIG. 4. The magnetization direction of
the magnetization pinned layer in the MR element R142 is the same
as the magnetization direction D112 of the magnetization pinned
layer in the MR element R112 shown in FIG. 4.
The magnetization directions of the magnetization pinned layers in
the MR elements R141 and R142 form a relative angle 2.phi.. The
magnetization direction of the magnetization pinned layer in the MR
element R141 is the direction rotated clockwise from the first
direction D1 by the angle .phi.. The magnetization direction of the
magnetization pinned layer in the MR element R142 is the direction
rotated counterclockwise from the first direction D1 by the angle
.phi..
Next, a description will be given of a plurality of MR elements
that form the first to fourth MR element rows R21, R22, R23, and
R24 of the bridge circuit 16. Each of the first to fourth MR
element rows R21, R22, R23, and R24 is composed of two MR elements
connected in series. The first MR element row R21 is composed of a
pair of MR elements R211 and R212. The second MR element row R22 is
composed of a pair of MR elements R221 and R222. The third MR
element row R23 is composed of a pair of MR elements R231 and R232.
The fourth MR element row R24 is composed of a pair of MR elements
R241 and R242.
One end of the MR element R211 serves as the first end of the first
MR element row R21. The other end of the MR element R211 is
connected to one end of the MR element R212. The other end of the
MR element R212 serves as the second end of the first MR element
row R21.
One end of the MR element R221 serves as the first end of the
second MR element row R22. The other end of the MR element R221 is
connected to one end of the MR element R222. The other end of the
MR element R222 serves as the second end of the second MR element
row R22.
One end of the MR element R231 serves as the first end of the third
MR element row R23. The other end of the MR element R231 is
connected to one end of the MR element R232. The other end of the
MR element R232 serves as the second end of the third MR element
row R23.
One end of the MR element R241 serves as the first end of the
fourth MR element row R24. The other end of the MR element R241 is
connected to one end of the MR element R242. The other end of the
MR element R242 serves as the second end of the fourth MR element
row R24.
Note that the MR elements R211 and R212 forming the first MR
element row R21 have only to be connected in series between the
first and second ends of the first MR element row R21, and may be
arranged in the order opposite to that of the example shown in FIG.
3. Likewise, two MR elements forming each of the other MR element
rows have only to be connected in series between the first and
second ends of the MR element row, and may be arranged in the order
opposite to that of the example shown in FIG. 3.
Now, a description will be given of the magnetization directions of
the magnetization pinned layers in the MR elements R211, R212,
R221, R222, R231, R232, R241, and R242. The magnetization
directions of the magnetization pinned layers in the pair of MR
elements R211 and R212 forming the first MR element row R21 are
pinned so that the intermediate direction between those
magnetization directions is the same as the second direction D2
(the Y direction). The magnetization directions of the
magnetization pinned layers in the pair of MR elements R241 and
R242 forming the fourth MR element row R24 are also pinned so that
the intermediate direction between those magnetization directions
is the same as the second direction D2. The magnetization direction
of the magnetization pinned layer in the MR element R241 is the
same as that of the magnetization pinned layer in the MR element
R211. The magnetization direction of the magnetization pinned layer
in the MR element R242 is the same as that of the magnetization
pinned layer in the MR element R212. The magnetization direction of
the magnetization pinned layers in the MR elements R211 and R241 is
the direction rotated counterclockwise by 90.degree. from the
magnetization direction D112 of the magnetization pinned layer in
the MR element R112 shown in FIG. 4. The magnetization direction of
the magnetization pinned layers in the MR elements R212 and R242 is
the direction rotated counterclockwise by 90.degree. from the
magnetization direction D111 of the magnetization pinned layer in
the MR element R111 shown in FIG. 4.
The magnetization directions of the magnetization pinned layers in
the MR elements R211 and R212 form a relative angle 2.phi.. The
magnetization directions of the magnetization pinned layers in the
MR elements R241 and R242 also form the relative angle 2.phi.. The
magnetization direction of the magnetization pinned layers in the
MR elements R211 and R241 is the direction rotated counterclockwise
from the second direction D2 by the angle .phi.. The magnetization
direction of the magnetization pinned layers in the MR elements
R212 and R242 is the direction rotated clockwise from the second
direction D2 by the angle .phi..
The magnetization directions of the magnetization pinned layers in
the pair of MR elements R221 and R222 forming the second MR element
row R22 are pinned so that the intermediate direction between those
magnetization directions is opposite to the second direction D2,
i.e., the -Y direction. The magnetization directions of the
magnetization pinned layers in the pair of MR elements R231 and
R232 forming the third MR element row R23 are also pinned so that
the intermediate direction between those magnetization directions
is opposite to the second direction D2. The magnetization direction
of the magnetization pinned layer in the MR element R231 is the
same as that of the magnetization pinned layer in the MR element
R221. The magnetization direction of the magnetization pinned layer
in the MR element R232 is the same as that of the magnetization
pinned layer in the MR element R222. The magnetization direction of
the magnetization pinned layers in the MR elements R221 and R231 is
opposite to the magnetization direction of the magnetization pinned
layers in the MR elements R212 and R242. The magnetization
direction of the magnetization pinned layers in the MR elements
R222 and R232 is opposite to the magnetization direction of the
magnetization pinned layers in the MR elements R211 and R241.
The magnetization directions of the magnetization pinned layers in
the MR elements R221 and R222 form a relative angle 2.phi.. The
magnetization directions of the magnetization pinned layers in the
MR elements R231 and R232 also form the relative angle 2.phi.. The
magnetization direction of the magnetization pinned layers in the
MR elements R221 and R231 is the direction rotated clockwise by the
angle .phi. from the direction opposite to the second direction D2.
The magnetization direction of the magnetization pinned layers in
the MR elements R222 and R232 is the direction rotated
counterclockwise by the angle .phi. from the direction opposite to
the second direction D2.
As described above, each MR element row in the first and second
detection circuits 11 and 12 is composed of a pair of MR elements
each having a magnetization pinned layer whose magnetization
direction is pinned in a predetermined direction. None of the first
to fourth MR element rows R11, R12, R13, and R14 in the first
detection circuit 11 includes any MR element that has a
magnetization pinned layer whose magnetization direction is pinned
in the first direction D1 (the X direction) or in the direction
opposite to the first direction D1 (the -X direction). None of the
first to fourth MR element rows R21, R22, R23, and R24 in the
second detection circuit 12 includes any MR element that has a
magnetization pinned layer whose magnetization direction is pinned
in the second direction D2 (the Y direction) or in the direction
opposite to the second direction D2 (the -Y direction).
In consideration of the production accuracy of the MR elements and
other factors, the magnetization directions of the magnetization
pinned layers in the plurality of MR elements in the detection
circuits 11 and 12 can be slightly different from the
above-described directions.
Reference is now made to FIG. 5A and FIG. 5B to describe an example
of two units that incorporate the bridge circuits 14 and 16 of the
rotating field sensor 1, respectively. FIG. 5A and FIG. 5B are plan
views showing an example of the units that incorporate the bridge
circuits 14 and 16, respectively. FIG. 5A shows a unit 40A
incorporating the bridge circuit 14. FIG. 5B shows a unit 40B
incorporating the bridge circuit 16. The unit 40A includes a
substrate 41A, and the bridge circuit 14 provided on the substrate
41A. The plurality of ports of the bridge circuit 14 are arranged
on the substrate 41A, near peripheral edges of the substrate 41A.
An MR element layout area of circular shape is provided on the
substrate 41A. The MR element layout area is circumferentially
divided into eight sections. The MR elements R111, R112, R121,
R122, R131, R132, R141, and R142 are located in the eight sections,
respectively. Wiring for electrically connecting the plurality of
MR elements to the plurality of ports is formed on the substrate
41A.
The unit 40B includes a substrate 41B, and the bridge circuit 16
provided on the substrate 41B. The plurality of ports of the bridge
circuit 16 are arranged on the substrate 41B, near peripheral edges
of the substrate 41B. An MR element layout area of circular shape
is provided on the substrate 41B. The MR element layout area is
circumferentially divided into eight sections. The MR elements
R211, R212, R221, R222, R231, R232, R241, and R242 are located in
the eight sections, respectively. Wiring for electrically
connecting the plurality of MR elements to the plurality of ports
is formed on the substrate 41B.
While FIG. 5A and FIG. 5B show the units 40A and 40B as separates
units, the units 40A and 40B may be integrated with each other. In
this case, the bridge circuits 14 and 16 may be arranged side by
side on a single substrate. Alternatively, the substrates 41A and
41B may be stacked on each other in the Z direction.
Reference is now made to FIG. 6 and FIG. 7 to describe an example
of the configuration of an arbitrary MR element in the units 40A
and 40B shown in FIG. 5A and FIG. 5B. FIG. 6 is a plan view showing
a plurality of lower electrodes that are arranged in a section
shown in FIG. 5A and FIG. 5B. FIG. 7 is a perspective view showing
a part of an MR element of FIG. 5A and FIG. 5B. In this example,
the MR element has a plurality of lower electrodes, a plurality of
MR films, and a plurality of upper electrodes. In a section on the
substrate 41A or 41B, the plurality of lower electrodes 42 are
arranged as shown in FIG. 6. Each being oblong in shape, the
plurality of lower electrodes 42 are arranged in a meandering
configuration as a whole. Two lower electrodes 42 adjoining in the
longitudinal direction of the lower electrodes 42 have a gap
therebetween. As shown in FIG. 7, MR films 50 are provided on the
top surfaces of the lower electrodes 42, near opposite ends in the
longitudinal direction. Each MR film 50 includes a free layer 51, a
nonmagnetic layer 52, a magnetization pinned layer 53, and an
antiferromagnetic layer 54 that are stacked in this order, the free
layer 51 being closest to the lower electrode 42. The free layer 51
is electrically connected to the lower electrode 42. The
antiferromagnetic layer 54 is made of an antiferromagnetic
material. The antiferromagnetic layer 54 is in exchange coupling
with the magnetization pinned layer 53 so as to pin the
magnetization direction of the magnetization pinned layer 53. The
plurality of upper electrodes 43 are arranged over the plurality of
MR films 50. Each upper electrode 43 is oblong in shape, and
establishes electrical connection between the respective
antiferromagnetic layers 54 of two adjoining MR films 50 that are
arranged on two lower electrodes 42 adjoining in the longitudinal
direction of the lower electrodes 42. Like the plurality of lower
electrodes 42, the plurality of upper electrodes 43 are arranged in
a meandering configuration as a whole. With such a configuration,
the plurality of MR films 50 in the MR element shown in FIG. 6 and
FIG. 7 are connected in series by the plurality of lower electrodes
42 and the plurality of upper electrodes 43. It should be
appreciated that the layers 51 to 54 of the MR films 50 may be
stacked in the order reverse to that shown in FIG. 7.
Now, a description will be given of the method by which the
arithmetic circuit 13 calculates the detected angle value .theta.s.
In the present embodiment, the second direction D2, which serves as
the reference direction when the second detection circuit 12
detects the rotating magnetic field MF, is orthogonal to the first
direction D1, which serves as the reference direction when the
first detection circuit 11 detects the rotating magnetic field MF.
Ideally, the first signal S1 output from the first detection
circuit 11 has a sine waveform that depends on the angle .theta.,
and the second signal S2 output from the second detection circuit
12 has a cosine waveform that depends on the angle .theta.. In this
case, the second signal S2 differs from the first signal S1 in
phase by 1/4 the signal period T, i.e., by .pi./2)(90.degree..
When the angle .theta. is greater than 0.degree. and smaller than
180.degree., the first signal S1 has a positive value. When the
angle .theta. is greater than 180.degree. and smaller than
360.degree., the first signal S1 has a negative value. When the
angle .theta. is equal to or greater than 0.degree. and smaller
than 90.degree. and when the angle .theta. is greater than
270.degree. and smaller than or equal to 360.degree., the second
signal S2 has a positive value. When the angle .theta. is greater
than 90.degree. and smaller than 270.degree., the second signal S2
has a negative value. The first signal S1 is a signal that
indicates the intensity of the component of the rotating magnetic
field MF in the first direction D1. The second signal S2 is a
signal that indicates the intensity of the component of the
rotating magnetic field MF in the second direction D2.
Based on the first signal S1 and the second signal S2, the
arithmetic circuit 13 calculates the detected angle value .theta.s
having a correspondence relationship with the angle .theta. that
the direction DM of the rotating magnetic field MF in the reference
position PR forms with respect to the reference direction DR.
Specifically, for example, the arithmetic circuit 13 calculates
.theta.s by the equation (1) below. Note that "a tan" represents an
arctangent. .theta.s=a tan(S1/S2) (1)
The term "a tan(S1/S2)" of the equation (1) represents the
arctangent calculation for determining .theta.s. Within the range
of 360.degree., .theta.s in the equation (1) has two solutions with
a difference of 180.degree. in value. Which of the two solutions of
.theta.s in the equation (1) is the true solution to .theta.s can
be determined from the combination of positive and negative signs
on S1 and S2. More specifically, if S1 is positive in value,
.theta.s is greater than 0.degree. and smaller than 180.degree.. If
S1 is negative in value, .theta.s is greater than 180.degree. and
smaller than 360.degree.. If S2 is positive in value, .theta.s is
equal to or greater than 0.degree. and smaller than 90.degree., or
is greater than 270.degree. and smaller than or equal to
360.degree.. If S2 is negative in value, .theta.s is greater than
90.degree. and smaller than 270.degree.. The arithmetic circuit 13
determines .theta.s in the range of 360.degree., using the equation
(1) and based on the foregoing determination of the combination of
positive and negative signs on S1 and S2.
The operation and effects of the rotating field sensor 1 will now
be described. In the rotating field sensor 1, the resistance of
each MR element periodically varies as the direction DM of the
rotating magnetic field MF rotates. The periodic variation in the
resistance of the MR element causes the potential difference across
the MR element to vary periodically. Ideally, a periodically
varying component of the resistance of the MR element has a
sinusoidal waveform (including a sine waveform and a cosine
waveform). Likewise, a periodically varying component of the
potential difference across the MR element ideally has a sinusoidal
waveform. In actuality, however, there are cases where the
magnetization direction of the magnetization pinned layer of the MR
element varies due to, for example, the influence of the rotating
magnetic field MF, and where the magnetization direction of the
free layer of the MR element does not coincide with the direction
of the rotating magnetic field MF due to the influence of the shape
anisotropy or coercivity of the free layer, for example. In such
cases, the waveforms of the periodically varying components
mentioned above are distorted from a sinusoidal curve.
In the present embodiment, the first signal S1 of the first
detection circuit 11 and the second signal S2 of the second
detection circuit 12 ideally have sinusoidal waveforms. However, if
the waveform of the periodically varying component of the potential
difference across each MR element is distorted as mentioned above,
the waveforms of the first signal S1 and the second signal S2 are
also distorted from a sinusoidal curve. As a result, the detected
angle value .theta.s calculated based on the first signal S1 and
the second signal S2 may possibly include an angular error with
respect to a theoretical value of the detected angle value .theta.s
that is expected when the direction DM of the rotating magnetic
field MF rotates ideally.
The distorted waveform of the periodically varying component of the
resistance of the MR element means that the periodically varying
component of the resistance of the MR element includes not only an
ideal sinusoidal component but also a harmonic component
(hereinafter referred to as the resistance harmonic component).
Likewise, the distorted waveform of the periodically varying
component of the potential difference across the MR element means
that the periodically varying component of the potential difference
across the MR element includes not only an ideal sinusoidal
component but also a harmonic component (hereinafter referred to as
the potential difference harmonic component). The potential
difference harmonic component results from the resistance harmonic
component. The magnitude of the potential difference harmonic
component is proportional to the magnitude of the resistance
harmonic component.
In the present embodiment, the first detection circuit 11 includes
the first and second MR element rows R11 and R12 connected in
series, and the third and fourth MR element rows R13 and R14
connected in series. The second detection circuit 12 includes the
first and second MR element rows R21 and R22 connected in series,
and the third and fourth MR element rows R23 and R24 connected in
series. Each MR element row is composed of a pair of MR elements
connected in series. The magnetization directions of the
magnetization pinned layers in two MR elements making up a pair
form a predetermined relative angle 2.phi. other than 0.degree. and
180.degree..
The potential difference across each MR element varies periodically
as the direction DM of the rotating magnetic field MF rotates. The
periodically varying component of the potential difference across
each MR element may include a potential difference harmonic
component in addition to an ideal sinusoidal component. In that
case, a periodically varying component of the potential difference
across an MR element row (a pair of MR elements) may also include a
potential difference harmonic component in addition to an ideal
sinusoidal component. The present embodiment allows the potential
difference harmonic component produced in one of two MR elements
making up a pair and that produced in the other of the two MR
elements to be combined with each other, thereby making the
potential difference harmonic component in an MR element row (a
pair of MR elements) smaller than that in each single MR element.
This will be discussed in more detail below.
First, a description will be made as to the resistance of the first
MR element row R11 shown in FIG. 4. Here, let R.sub.11, Ra, and Rb
be the resistance of the first MR element row R11, the resistance
of the MR element R111, and the resistance of the MR element R112,
respectively. Each of the resistances Ra and Rb includes a periodic
component which varies periodically as the direction DM of the
rotating magnetic field MF rotates, and an initial component that
is independent of the variation in the direction DM of the rotating
magnetic field MF. The periodic component includes an ideal
component, i.e., an ideal sinusoidal component, and a resistance
harmonic component that distorts the waveform of the periodic
component. The following description assumes that the ideal
components are of the same amplitude in all the MR elements
included in the rotating field sensor 1. It is also assumed that
the initial components are equal in all the MR elements included in
the rotating field sensor 1.
As shown in FIG. 4, the magnetization direction D111 of the
magnetization pinned layer in the MR element R111 is the direction
rotated clockwise from the first direction D1 by the angle .phi..
Accordingly, the ideal component and the resistance harmonic
component of the MR element R111 are a periodic function of a
variable .theta. with an initial phase of -.phi.. Letting .alpha.
be the amplitude of the ideal component and .beta. be the initial
component, the resistance Ra of the MR element R111 is expressed by
the following equation (2).
Ra=-.alpha.sin(.theta.-.phi.)-e(.theta.-.phi.)+.beta. (2)
In the equation (2), -.alpha.sin(.theta.-.phi.) (represents the
ideal component, and -e(.theta.-.phi.) represents the resistance
harmonic component which is the periodic function of the variable
.theta. with an initial phase of -.phi..
As shown in FIG. 4, the magnetization direction D112 of the
magnetization pinned layer in the MR element R112 is the direction
rotated counterclockwise from the first direction D1 by the angle
.phi.. Accordingly, the ideal component and the resistance harmonic
component of the MR element R112 are a periodic function of the
variable .theta. with an initial phase of .phi.. The resistance Rb
of the MR element R112 is expressed by the following equation (3).
Rb=-.alpha.sin(.theta.+.phi.)-e(.theta.+.phi.)+.beta. (3)
In the equation (3), -.alpha.sin(.theta.+.phi.) represents the
ideal component, and -e(.theta.+.phi.) represents the resistance
harmonic component which is the periodic function of the variable
.theta. with an initial phase of .phi..
Using the equations (2) and (3), the resistance R.sub.11 of the
first MR element row R11 is expressed by the following equation
(4).
.times..times..alpha..function..theta..PHI..function..theta..PHI..beta..t-
imes..alpha..function..theta..PHI..function..theta..PHI..beta..times..alph-
a..function..theta..PHI..function..theta..PHI..times..function..theta..PHI-
..function..theta..PHI..times..beta..times..times..alpha..times..times..PH-
I..times..times..theta..function..theta..PHI..function..theta..PHI..times.-
.beta. ##EQU00001##
Next, the resistance R.sub.12 of the second MR element row R12 and
the resistance R.sub.13 of the third MR element row R13 will be
described. As previously described, the magnetization direction of
the magnetization pinned layers in the MR elements R121 and R131 is
opposite to the magnetization direction D111 of the magnetization
pinned layer in the MR element R111 shown in FIG. 4. The
magnetization direction of the magnetization pinned layers in the
MR elements R122 and R132 is opposite to the magnetization
direction D112 of the magnetization pinned layer in the MR element
R112 shown in FIG. 4. Therefore, the resistance R.sub.12 of the
second MR element row R12 and the resistance R13 of the third MR
element row R13 are expressed by the following equation (5).
.times..times..alpha..function..theta..PHI..function..theta..PHI..beta..t-
imes..alpha..function..theta..PHI..function..theta..PHI..beta..times..alph-
a..function..theta..PHI..function..theta..PHI..times..function..theta..PHI-
..function..theta..PHI..times..beta..times..times..alpha..times..times..PH-
I..times..times..theta..function..theta..PHI..function..theta..PHI..times.-
.beta. ##EQU00002##
Next, the resistance R.sub.14 of the fourth MR element row R14 will
be described. As previously described, the magnetization direction
of the magnetization pinned layer in the MR element R141 is the
same as the magnetization direction D111 of the magnetization
pinned layer in the MR element R111 shown in FIG. 4. The
magnetization direction of the magnetization pinned layer in the MR
element R142 is the same as the magnetization direction D112 of the
magnetization pinned layer in the MR element R112 shown in FIG. 4.
Therefore, the resistance R.sub.14 of the fourth MR element row R14
is equal to the resistance R.sub.11 of the first MR element row R11
expressed by the equation (4).
Next, the resistance R.sub.21 of the first MR element row R21 and
the resistance R.sub.24 of the fourth MR element row R24 will be
described. As previously described, the magnetization direction of
the magnetization pinned layers in the MR elements R211 and R241 is
the direction rotated counterclockwise by 90.degree. from the
magnetization direction D112 of the magnetization pinned layer in
the MR element R112 shown in FIG. 4. The magnetization direction of
the magnetization pinned layers in the MR elements R212 and R242 is
the direction rotated counterclockwise by 90.degree. from the
magnetization direction D111 of the magnetization pinned layer in
the MR element R111 shown in FIG. 4. Therefore, the resistance R21
of the first MR element row R21 and the resistance R.sub.24 of the
fourth MR element row R24 are expressed by the following equation
(6).
.times..times..alpha..function..theta..PHI..function..theta..PHI..beta..t-
imes..alpha..function..theta..PHI..function..theta..PHI..beta..times..alph-
a..function..theta..PHI..function..theta..PHI..times..function..theta..PHI-
..function..theta..PHI..times..beta..times..times..alpha..times..times..PH-
I..times..times..theta..function..theta..PHI..function..theta..PHI..times.-
.beta. ##EQU00003##
In the equation (6), f(.theta.-.phi.) represents the resistance
harmonic component which is the periodic function of the variable
.theta. with an initial phase of -.phi., and f(.theta.+.phi.)
represents the resistance harmonic component which is the periodic
function of the variable .theta. with an initial phase of
.phi..
Next, the resistance R.sub.22 of the second MR element row R22 and
the resistance R.sub.23 of the third MR element row R23 will be
described. As previously described, the magnetization direction of
the magnetization pinned layers in the MR elements R221 and R231 is
opposite to the magnetization direction of the magnetization pinned
layers in the MR elements R212 and R242. The magnetization
direction of the magnetization pinned layers in the MR elements
R222 and R232 is opposite to the magnetization direction of the
magnetization pinned layers in the MR elements R211 and R241.
Therefore, the resistance R.sub.22 of the second MR element row R22
and the resistance R23 of the third MR element row R23 are
expressed by the following equation (7).
.times..times..alpha..function..theta..PHI..function..theta..PHI..beta..t-
imes..alpha..function..theta..PHI..function..theta..PHI..beta..times..alph-
a..function..theta..PHI..function..theta..PHI..times..function..theta..PHI-
..function..theta..PHI..times..beta..times..times..alpha..times..times..PH-
I..times..times..theta..function..theta..PHI..function..theta..PHI..times.-
.beta. ##EQU00004##
As can be seen from the equations (4) to (7), the ideal component
of the resistance of each MR element row is a sine or cosine
function of the variable .theta. with an initial phase of 0. Now,
consider a virtual MR element that has a magnetization pinned layer
whose magnetization direction is the intermediate direction between
the magnetization directions of the magnetization pinned layers of
two MR elements forming an MR element row. The phase of the ideal
component of the resistance of each MR element row is the same as
that of the ideal component of the resistance of the aforementioned
virtual MR element. Consequently, according to the present
embodiment, the first detection circuit 11 is able to detect the
intensity of the component of the rotating magnetic field MF in the
first direction D1 and to output the first signal S1 indicating the
intensity even if the first detection circuit 11 does not include
any MR element that has a magnetization pinned layer whose
magnetization direction is pinned in the first direction D1 or in
the direction opposite to the first direction D1. Likewise, the
second detection circuit 12 is able to detect the intensity of the
component of the rotating magnetic field MF in the second direction
D2 and to output the second signal S2 indicating the intensity even
if the second detection circuit 12 does not include any MR element
that has a magnetization pinned layer whose magnetization direction
is pinned in the second direction D2 or in the direction opposite
to the second direction D2.
Now, a description will be made as to the resistance harmonic
component of an MR element row. Like the resistance of an MR
element, the resistance of an MR element row includes a periodic
component and an initial component. The periodic component includes
an ideal component and a resistance harmonic component. The term
-{e(.theta.-.phi.)+e(.theta.+.phi.)} in the equation (4) represents
the resistance harmonic component in the first and fourth MR
element rows R11 and R14. This is a combination of the resistance
harmonic components -e(.theta.-.phi.) and -e(.theta.+.phi.) of two
MR elements that form each of the MR element rows R11 and R14. The
term e(.theta.+.phi.)+e(.theta.+.phi.) in the equation (5)
represents the resistance harmonic component in the second and
third MR element rows R12 and R13. This is a combination of the
resistance harmonic components e(.theta.-.phi.) and
e(.theta.+.phi.) of two MR elements that form each of the MR
element rows R12 and R13. The term
-{f(.theta.-.phi.)+f(.theta.+.phi.)} in the equation (6) represents
the resistance harmonic component in the first and fourth MR
element rows R21 and R24. This is a combination of the resistance
harmonic components -f(.theta.-.phi.) and -f(.theta.+.phi.) of two
MR elements that form each of the MR element rows R21 and R24. The
term f(.theta.-.phi.)+f(.theta.+.phi.) in the equation (7)
represents the resistance harmonic component in the second and
third MR element rows R22 and R23. This is a combination of the
resistance harmonic components f(.theta.-.phi.) and
f(.theta.+.phi.) of two MR elements that form each of the MR
element rows R22 and R23.
In the present embodiment, .phi. is selected so that the maximum
absolute value of the resistance harmonic component of an MR
element row is smaller than the maximum absolute value of the
resistance harmonic component of an MR element. More specifically,
.phi. is selected so that the maximum absolute value of
{e(.theta.-.phi.)+e(.theta.+.phi.)} in the equations (4) and (5) is
smaller than the maximum absolute value of e(.theta.-.phi.) and the
maximum absolute value of e(.theta.+.phi.), and so that the maximum
absolute value of {f(.theta.-.phi.)+f(.theta.+.phi.)} in the
equations (6) and (7) is smaller than the maximum absolute value of
f(.theta.-.phi.) and the maximum absolute value of
f(.theta.+.phi.). Selecting .phi. in this manner allows the maximum
absolute value of the potential difference harmonic component of an
MR element row to be smaller than the maximum absolute value of the
potential difference harmonic component of an MR element. Note that
the potential difference harmonic component of an MR element row is
a combination of the potential difference harmonic components of
two MR elements that form the MR element row. In the present
embodiment, in particular, .phi. is preferably selected so that the
maximum absolute value of the resistance harmonic component of an
MR element row is minimized.
As described above, the present embodiment allows the potential
difference harmonic components in two MR elements that form an MR
element row to be combined with each other, thereby making the
potential difference harmonic component in the MR element row
smaller than that in each single MR element. According to the
present embodiment, it is thus possible to prevent the waveform of
the first signal S1 of the first detection circuit 11 and the
waveform of the second signal S2 of the second detection circuit 12
from being distorted from a sinusoidal curve. This makes it
possible to reduce errors in the angle detected by the rotating
field sensor 1.
Now, a description will be given of a specific example of .phi. at
which the maximum absolute value of the resistance harmonic
component of an MR element row is minimized. First, a case will be
described where the resistance harmonic component of an MR element
includes only a third harmonic component relative to the ideal
component. Here, by way of example, letting .gamma. represent the
amplitude of the third harmonic component, e(.theta.-.phi.) in the
equations (4) and (5) will be expressed as -.gamma.sin
3(.theta.-.phi.); e(.theta.+.phi.) in the equations (4) and (5)
will be expressed as -.gamma.sin 3(.theta.+.phi.); f(.theta.-.phi.)
in the equations (6) and (7) will be expressed as .gamma.cos
3(.theta.-.phi.); and f(.theta.+.phi.) in the equations (6) and (7)
will be expressed as .gamma.cos 3(.theta.+.phi.). In this case, in
the equations (4) and (5), it holds that
e(.theta.+.phi.)+e(.theta.-.phi.)=-2.gamma.cos 3.phi.sin 3.theta..
Furthermore, in the equations (6) and (7), it holds that
f(.theta.+.phi.)+f(.theta.-.phi.)=2.gamma.cos 3.phi.cos 3.theta..
Here, if we set .phi.=.pi./6 (30.degree.), then
e(.theta.+.phi.)+e(.theta.-.phi.) in the equations (4) and (5) and
f(.theta.+.phi.)+f(.theta.-.phi.) in the equations (6) and (7) are
both zero. Accordingly, if the resistance harmonic component of an
MR element includes only the third harmonic component, letting
.phi.=.pi./6 makes the maximum absolute value of the resistance
harmonic component of an MR element row be zero (the minimum).
Each of FIG. 8 and FIG. 9 is a waveform chart showing an example of
the waveform of the periodically varying component of the potential
difference across an MR element. The waveforms shown in FIG. 8 and
FIG. 9 are those obtained in the case where the resistance harmonic
component of the MR element includes only the third harmonic
component. FIG. 8 and FIG. 9 illustrate that letting .phi.=.pi./6
leads to a reduction in the potential difference harmonic component
in an MR element row. Portion (a) of FIG. 8 shows the waveform of
the periodically varying component of the potential difference
across the MR element R121. Portion (b) of FIG. 8 shows the
waveform of the periodically varying component of the potential
difference across the MR element R122. Portion (a) of FIG. 9 shows
the waveform of the periodically varying component of the potential
difference across the MR element R221. Portion (b) of FIG. 9 shows
the waveform of the periodically varying component of the potential
difference across the MR element R222. In FIG. 8 and FIG. 9, the
horizontal axis represents the angle .theta., while the vertical
axis represents the normalized output. The normalized output on the
vertical axis indicates the values of the potential difference
where the maximum value of the ideal sinusoidal component included
in the periodically varying component of the potential difference
is assumed as 1. Reference numerals 60, 65, 70, and 75 indicate the
waveforms of the periodically varying components of the potential
differences across the respective MR elements. Reference numerals
61, 66, 71, and 76 each indicate an ideal sinusoidal curve.
Reference numerals 63, 68, 73, and 78 indicate the waveforms of the
potential difference harmonic components corresponding to the
resistance harmonic components in the respective MR elements. The
waveforms shown in FIG. 8 and FIG. 9 were generated by
simulation.
The periodically varying components (reference numerals 60, 65, 70,
and 75) of the potential differences have a period equal to the
signal period T of the first and second signals S1 and S2. In the
examples shown in FIG. 8 and FIG. 9, the potential difference
harmonic components (reference numerals 63, 68, 73, and 78)
corresponding to the resistance harmonic components (the third
harmonic components) in the MR elements vary with a period of 1/3
the signal period T, i.e., with a period of 2.pi./3 (120.degree.)
in synchronization with the periodically varying components of the
potential differences. In this case, the waveforms of the
periodically varying components of the potential differences are
distorted as shown in FIG. 8 and FIG. 9.
Note that examples where the waveform of the periodically varying
component of the potential difference is distorted from a
sinusoidal curve due to the third resistance harmonic component are
not limited to those shown in FIG. 8 and FIG. 9. In the examples
shown in FIG. 8 and FIG. 9, the waveforms of the periodically
varying components of the potential differences are each distorted
from the ideal sinusoidal curve so as to approach a triangular
waveform. Unlike the examples shown in FIG. 8 and FIG. 9, however,
the third resistance harmonic component may also cause the waveform
of the periodically varying component of the potential difference
to be distorted from the ideal sinusoidal curve to approach a
rectangular waveform. A description will be made later as to an
example where the resistance harmonic component of an MR element
includes a second harmonic component.
As described above, if the resistance harmonic component of an MR
element includes only the third harmonic component, the maximum
absolute value of the resistance harmonic component of an MR
element row is minimized when .phi.=.pi./6 (30.degree.). FIG. 8 and
FIG. 9 show that letting .phi.=.pi./6 leads to a reduction in the
potential difference harmonic component in an MR element row. As
shown in FIG. 8, the potential difference harmonic component of the
MR element R121 (reference numeral 63) and the potential difference
harmonic component of the MR element R122 (reference numeral 68)
have opposite phases. In the present embodiment, the MR elements
R121 and R122 are connected in series between the first end and the
second end of the second MR element row R12. This causes the
potential difference harmonic components of the MR elements R121
and R122 to cancel each other out in the second MR element row R12.
Consequently, as compared with the MR elements R121 and R122, the
second MR element row R12 achieves a reduction in the potential
difference harmonic component.
As shown in FIG. 9, the potential difference harmonic component of
the MR element R221 (reference numeral 73) and the potential
difference harmonic component of the MR element R222 (reference
numeral 78) have opposite phases. In the present embodiment, the MR
elements R221 and R222 are connected in series between the first
end and the second end of the second MR element row R22. This
causes the potential difference harmonic components of the MR
elements R221 and R122 to cancel each other out in the second MR
element row R22. Consequently, as compared with the MR elements
R221 and R222, the second MR element row R22 achieves a reduction
in the potential difference harmonic component.
FIG. 10 is a waveform chart showing the waveform of a periodically
varying component of the potential difference across a pair of MR
elements. In FIG. 10, the horizontal axis indicates the angle
.theta., while the vertical axis indicates the normalized output in
like manner with FIG. 8 and FIG. 9. Reference numeral 91 indicates
the waveform of the periodically varying component of the potential
difference across a pair of MR elements R121 and R122, i.e., the
potential difference between the first and second ends of the
second MR element row R12. Reference numeral 92 indicates the
waveform of the periodically varying component of the potential
difference across a pair of MR elements R221 and R222, i.e., the
potential difference between the first and second ends of the
second MR element row R22. As shown in FIG. 10, because of the
cancellation of the potential difference harmonic components of the
MR elements R121 and R122, the periodically varying component of
the potential difference denoted by reference numeral 91 has a
sinusoidal waveform with reduced distortion, i.e., with a reduced
potential difference harmonic component. Likewise, because of the
cancellation of the potential difference harmonic components of the
MR elements R221 and R222, the periodically varying component of
the potential difference denoted by reference numeral 92 has a
sinusoidal waveform with reduced distortion, i.e., with a reduced
potential difference harmonic component.
It is also possible for the other MR element rows to achieve a
reduction in the potential difference harmonic component in the MR
element row as compared with that of each individual MR element
constituting the MR element row.
Now, a description will be made as to the case where the resistance
harmonic component of an MR element includes second and third
harmonic components relative to the ideal component. The following
describes the results of a first simulation that was carried out
for determining the value of .phi. at which the magnitude of the
resistance harmonic component in an MR element row is minimized in
the case where the resistance harmonic component of an MR element
includes the second and third harmonic components. Such a value of
.phi. will hereinafter be represented by .phi.t. In the first
simulation, the ratio of the amplitude of the second harmonic
component and the ratio of the amplitude of the third harmonic
component to the amplitude of the ideal component were varied to
determine .phi.t. Here, the ratio of the amplitude of the second
harmonic component to the amplitude of the ideal component will be
represented by p1 and the ratio of the amplitude of the third
harmonic component to the amplitude of the ideal component will be
represented by p2. In the first simulation, the ratio p1 of the
amplitude of the second harmonic component was varied in increments
of 1% within the range from 0% to 10%. On the other hand, the ratio
p2 of the amplitude of the third harmonic component was varied in
increments of 0.1% within the range from 0.1% to 1%. Then, .phi.t
was determined for all the combinations of p1 and p2. More
specifically, e(.theta.+.phi.)+e(.theta.-.phi.) in the equations
(4) and (5) and f(.theta.+.phi.)+f(.theta.-.phi.) in the equations
(6) and (7) were each expressed as a function that includes the
second harmonic component and the third harmonic component, and
then .phi. at which the maximum absolute value of these functions
is minimized was determined as .phi.t.
FIG. 11 shows the values of .phi.t determined by the first
simulation. In FIG. 11, the horizontal axis indicates the ratio p2
of the amplitude of the third harmonic component, while the
vertical axis indicates .phi.t. FIG. 11 shows that when the ratio
p1 of the amplitude of the second harmonic component is 0% (when no
second harmonic component is included), .phi.t is 30.degree.
(.pi./6) regardless of the ratio p2 of the amplitude of the third
harmonic component. FIG. 11 also shows that when p1 is other than
0% and p2 is somewhat high, .phi.t becomes closer to 30.degree.
(.pi./6) with increasing P2 and with decreasing P1.
Now, a description will be given of simulation results showing that
the present embodiment allows reducing the error in the angle
detected by the rotating field sensor 1. The following describes
the results of a second simulation in which a rotating field sensor
of a comparative example and the rotating field sensor 1 according
to the present embodiment were compared in terms of angular error.
The configuration of the rotating field sensor of the comparative
example will be described first. Like the rotating field sensor 1
according to the present embodiment, the rotating field sensor of
the comparative example includes first and second detection
circuits and an arithmetic circuit. The first detection circuit of
the comparative example has a first bridge circuit composed of four
MR elements, instead of the bridge circuit 14 shown in FIG. 3. The
second detection circuit of the comparative example has a second
bridge circuit composed of four MR elements, instead of the bridge
circuit 16 shown in FIG. 3. Each of the magnetization pinned layers
in the four MR elements forming the first bridge circuit has a
magnetization direction the same as or opposite to the first
direction D1. Each of the magnetization pinned layers in the four
MR elements forming the second bridge circuit has a magnetization
direction the same as or opposite to the second direction D2. The
remainder of the configuration of the rotating field sensor of the
comparative example is the same as that of the rotating field
sensor 1 according to the present embodiment.
In the second simulation, the ratio p1 of the amplitude of the
second harmonic component and the ratio p2 of the amplitude of the
third harmonic component were varied in the same manner as in the
first simulation to determine an angular error included in the
detected angle value .theta.s for each of the rotating field sensor
of the comparative example and the rotating field sensor 1
according to the present embodiment. More specifically, the angular
error was identified as the difference between the detected angle
value .theta.s calculated by the equation (1) and a theoretical
value of the detected angle value .theta.s that is expected when
the direction DM of the rotating magnetic field MF rotates ideally.
Note that the resistance expressed by the equations (4) to (7) with
.phi.=0 was employed as the resistance of the MR element in the
rotating field sensor of the comparative example. For the rotating
field sensor 1 according to the embodiment, .phi.t determined by
the first simulation was applied. More specifically, the resistance
expressed by the equations (4) to (7) with .phi.=.phi.t was
employed as the resistance of the MR element row in the rotating
field sensor 1 according to the embodiment.
FIG. 12 and FIG. 13 show the angular errors determined by the
second simulation. FIG. 12 shows the angular error for the rotating
field sensor of the comparative example. FIG. 13 shows the angular
error for the rotating field sensor 1 according to the present
embodiment. In FIG. 12 and FIG. 13, the horizontal axis indicates
the ratio p2 of the third harmonic component, and the vertical axis
indicates .phi.t. FIG. 12 and FIG. 13 show that where the ratio p1
of the amplitude of the second harmonic component and the ratio p2
of the third harmonic component are varied, the angular error
caused by the rotating field sensor of the comparative example is
0.6.degree. or less, whereas the angular error caused by the
rotating field sensor 1 according to the embodiment is 0.2.degree.
or less. The second simulation shows that according to the present
embodiment, selecting the optimum value of .phi., i.e., .phi.t
makes it possible to reduce the error in the angle detected by the
rotating field sensor 1. For the actual rotating field sensor 1,
the optimum value of .phi. may be selected according to the service
conditions in which the rotating field sensor 1 is used.
Now, a description will be given of the results of first and second
experiments that were carried out to verify the results of the
aforementioned second simulation. In the first experiment, a
plurality of rotating field sensors 1 with different values of
.phi. were actually fabricated to examine the relationship between
.phi. and the angular error. In the first experiment, five rotating
field sensors 1 were fabricated with .phi. set to 19.degree.,
21.degree., 23.degree., 30.degree., and 45.degree. to examine the
maximum angular error value. The intensity of the rotating magnetic
field MF was set to 400 Oe (1 Oe=79.6 A/m) in the first experiment.
FIG. 14 shows the results of the first experiment. In FIG. 14, the
horizontal axis indicates .phi. and the vertical axis indicates the
angular error. FIG. 14 shows that the angular error differs
depending on .phi. and can be reduced by selecting the optimum
value of .phi.. Of the five rotating field sensors 1 fabricated for
the first experiment, the one with .phi. of 23.degree. was found to
have the minimum angular error.
In the second experiment, the rotating field sensor 1 which was
fabricated for the first experiment with .phi.=23.degree.
(hereinafter referred to as the rotating field sensor 1 of the
practical example) and a rotating field sensor of a comparative
example were used to examine the relationship between the intensity
of the rotating magnetic field MF and the angular error. The
rotating field sensor of the comparative example used for the
second experiment has the same configuration as that of the
rotating field sensor of the comparative example used for the
second simulation. In the second experiment, for the rotating field
sensor of the comparative example and the rotating field sensor 1
of the practical example, the intensity of the rotating magnetic
field MF was varied in increments of 100 Oe within the range from
100 Oe to 700 Oe to examine the angular error at each intensity.
FIG. 15 and FIG. 16 show the results of the second experiment. FIG.
15 shows the results for the rotating field sensor of the
comparative example, while FIG. 16 shows the results for the
rotating field sensor 1 of the practical example. In FIG. 15 and
FIG. 16, the horizontal axis indicates the angle .theta. and the
vertical axis indicates the angular error. FIG. 15 and FIG. 16
indicate that the rotating field sensor 1 of the practical example
shows smaller angular errors than those of the rotating field
sensor of the comparative example over a wide range of intensity of
the rotating magnetic field MF. The second experiment shows that
selecting the optimum value of .phi. allows a reduction in the
angular error regardless of the intensity of the rotating magnetic
field MF.
Other effects provided by the present embodiment will now be
described. In the present embodiment, the first detection circuit
11 detects the intensity of the component of the rotating magnetic
field MF in the first direction D1 and outputs the first signal S1
indicating the intensity. However, none of the first to fourth MR
element rows R11, R12, R13, and R14 in the first detection circuit
11 includes any MR element that has a magnetization pinned layer
whose magnetization direction is pinned in the first direction D1
or in the direction opposite to the first direction D1. The second
detection circuit 12 detects the intensity of the component of the
rotating magnetic field MF in the second direction D2 and outputs
the second signal S2 indicating the intensity. However, none of the
first to fourth MR element rows R21, R22, R23, and R24 in the
second detection circuit 12 includes any MR element that has a
magnetization pinned layer whose magnetization direction is pinned
in the second direction D2 or in the direction opposite to the
second direction D2. As compared with a case where the first
detection circuit 11 includes an MR element that has a
magnetization pinned layer whose magnetization direction is pinned
in the first direction D1 or in the direction opposite to the first
direction D1 while the second detection circuit 12 includes an MR
element that has a magnetization pinned layer whose magnetization
direction is pinned in the second direction D2 or in the direction
opposite to the second direction D2, the present embodiment makes
it possible to reduce the number of MR elements to be included in
each of the detection circuits 11 and 12, and makes it easier to
design the detection circuits 11 and 12. As such, the present
embodiment provides a simplified configuration while allowing a
reduction in the error in the detected angle.
To reduce the angular error of a rotating field sensor, the
following method is also conceivable. The method employs a third
detection circuit and a fourth detection circuit in addition to the
first and second detection circuits of the aforementioned
comparative example. The third detection circuit has the same
configuration as that of the first detection circuit of the
comparative example, and outputs a signal that has a predetermined
phase difference with respect to the output signal of the first
detection circuit of the comparative example. The fourth detection
circuit has the same configuration as that of the second detection
circuit of the comparative example, and outputs a signal that has a
predetermined phase difference with respect to the output signal of
the second detection circuit of the comparative example. The
detected angle value is calculated based on a signal obtained by
combining the output signals of the first and third detection
circuits and a signal obtained by combining the output signals of
the second and fourth detection circuits. This method, however, has
the problem that the presence of the four detection circuits
increases the rotating field sensor in size, and the problem that
the operation for processing the output signals of the four
detection circuits also increases in complexity.
In contrast to this, the present embodiment does not require the
aforementioned third and fourth detection circuits and allows
reducing the potential difference harmonic component in each pair
of MR elements (each MR element row). As compared with the
aforementioned method, the present embodiment thus allows the
rotating field sensor to be smaller in size and also reduces
computational complexity.
Furthermore, in the present embodiment, two MR elements making up a
pair can be formed to have the same configuration except the
magnetization direction of the magnetization pinned layer. For this
reason, even if the potential difference harmonic component of each
MR element is a function of temperature, variations caused by the
temperature in the respective potential difference harmonic
components of the two MR elements are equalized. Thus, when the
potential difference harmonic components of the two MR elements are
combined together, the potential difference harmonic component in
the MR element row becomes smaller than that of each single MR
element. Consequently, according to the present embodiment, it is
eventually possible to obtain a detected angle value with less
temperature-based error variations.
Modification Examples
Reference is now made to FIG. 17 and FIG. 18 to describe a first
and a second modification example of the present embodiment. The
first modification example will be described first, with reference
to FIG. 17. FIG. 17 is an explanatory diagram showing the
configuration of a rotating field sensor of the first modification
example. In FIG. 17, a magnet 3 including one or more pairs of N
and S poles alternately arranged in a ring shape is shown as an
example of the means for generating a rotating magnetic field whose
direction rotates. In the example shown in FIG. 17, the magnet 3
includes two pairs of N and S poles. The rotating field sensor 1 of
the first modification example detects the direction of the
rotating magnetic field generated from the outer periphery of the
magnet 3. In the example shown in FIG. 17, the plane of the drawing
of FIG. 17 is an XY plane, and the direction perpendicular to the
plane is the Z direction. The N and S poles of the magnet 3 are
arranged symmetrically with respect to the center of rotation
parallel to the Z direction. The magnet 3 rotates about the center
of rotation. As a result, a rotating magnetic field occurs based on
the magnetic field generated by the magnet 3. The rotating magnetic
field rotates about the center of rotation (the Z direction). In
the example shown in FIG. 17, the magnet 3 rotates in a
counterclockwise direction, and the rotating magnetic field rotates
in a clockwise direction.
In the example shown in FIG. 17, the reference direction DR is set
to a radial direction of the magnet 3. Although not shown in the
drawings, the rotating field sensor 1 detects a component of the
rotating magnetic field in a first direction and a component of the
rotating magnetic field in a second direction. The relationships
between the reference direction DR and the first and second
directions are the same as the relationships between the reference
direction DR and the first and second directions D1 and D2 shown in
FIG. 2.
The second modification example of the embodiment will now be
described with reference to FIG. 18. FIG. 18 is an explanatory
diagram showing the configuration of a rotating field sensor of the
second modification example. In FIG. 18, a magnet 4 including a
plurality of pairs of N and S poles alternately arranged in a line
is shown as an example of the means for generating a rotating
magnetic field whose direction rotates. The rotating field sensor 1
of the second modification example detects the direction of the
rotating magnetic field generated from the outer periphery of the
magnet 4. In the example shown in FIG. 18, the plane of the drawing
of FIG. 18 is an XY plane, and the direction perpendicular to the
plane is the Z direction. The magnet 4 makes a straight movement in
its longitudinal direction along with a straight movement of an
object. As a result, a rotating magnetic field occurs based on the
magnetic field generated by the magnet 4. The rotating magnetic
field rotates about the Z direction.
In the example shown in FIG. 18, the reference direction DR is set
to a direction orthogonal to the direction of movement of the
magnet 4 in the XY plane. Although not shown in the drawings, the
rotating field sensor 1 detects a component of the rotating
magnetic field in a first direction and a component of the rotating
magnetic field in a second direction. The relationships between the
reference direction DR and the first and second directions are the
same as the relationships between the reference direction DR and
the first and second directions D1 and D2 shown in FIG. 2.
Second Embodiment
A rotating field sensor according to a second embodiment of the
invention will now be described. The rotating field sensor
according to the second embodiment has the same circuit
configuration as that of the rotating field sensor 1 according to
the first embodiment shown in FIG. 3.
As described in relation to the first embodiment, in the first
detection circuit 11, the magnetization directions of the
magnetization pinned layers in the MR elements R131 and R132
forming the third MR element row R13 are the same as those of the
magnetization pinned layers in the MR elements R121 and R122
forming the second MR element row R12. Furthermore, in the first
detection circuit 11, the magnetization directions of the
magnetization pinned layers in the MR elements R141 and R142
forming the fourth MR element row R14 are the same as those of the
magnetization pinned layers in the MR elements R111 and R112
forming the first MR element row R11.
In the second detection circuit 12, the magnetization directions of
the magnetization pinned layers in the MR elements R231 and R232
forming the third MR element row R23 are the same as those of the
magnetization pinned layers in the MR elements R221 and R222
forming the second MR element row R22. Furthermore, in the second
detection circuit 12, the magnetization directions of the
magnetization pinned layers in the MR elements R241 and R242
forming the fourth MR element row R24 are the same as those of the
magnetization pinned layers in the MR elements R211 and R212
forming the first MR element row R21.
In the present embodiment, MR elements that are included in two
respective different MR element rows and provided with
magnetization pinned layers having the same magnetization direction
are disposed adjacent to each other. More specifically, in the
first detection circuit 11, MR elements that are included in the
first MR element row R11 and the fourth MR element row R14
respectively and provided with magnetization pinned layers having
the same magnetization direction are disposed adjacent to each
other, while MR elements that are included in the second MR element
row R12 and the third MR element row R13 respectively and provided
with magnetization pinned layers having the same magnetization
direction are disposed adjacent to each other. In the second
detection circuit 12, MR elements that are included in the first MR
element row R21 and the fourth MR element row R24 respectively and
provided with magnetization pinned layers having the same
magnetization direction are disposed adjacent to each other, while
MR elements that are included in the second MR element row R22 and
the third MR element row R23 respectively and provided with
magnetization pinned layers having the same magnetization direction
are disposed adjacent to each other.
FIG. 19 is a plan view of a unit 40 that incorporates the bridge
circuits 14 and 16 shown in FIG. 3. The unit 40 includes a
substrate 41 with the bridge circuits 14 and 16 provided thereon.
The bridge circuit 14 is located on the lower side in FIG. 19. The
bridge circuit 16 is located on the upper side in FIG. 19. The
plurality of ports of the bridge circuits 14 and 16 are arranged on
the substrate 41, near peripheral edges of the substrate 41.
The bridge circuit 14 has four MR element layout areas 141, 142,
143, and 144. Two MR elements are located in each of the MR element
layout areas 141 to 144. In the MR element layout areas 141 and
142, MR elements that are included in the first MR element row R11
and the fourth MR element row R14 respectively and provided with
magnetization pinned layers having the same magnetization direction
are disposed adjacent to each other. In the MR element layout areas
143 and 144, MR elements that are included in the second MR element
row R12 and the third MR element row R13 respectively and provided
with magnetization pinned layers having the same magnetization
direction are disposed adjacent to each other. Note that the
numerical value in each of the MR element layout areas 141 to 144
shows an example of the angle that the magnetization direction of
the magnetization pinned layer of the MR element forms with respect
to the reference direction DR.
The bridge circuit 16 has four MR element layout areas 161, 162,
163, and 164. Two MR elements are located in each of the MR element
layout areas 161 to 164. In the MR element layout areas 161 and
162, MR elements that are included in the first MR element row R21
and the fourth MR element row R24 respectively and provided with
magnetization pinned layers having the same magnetization direction
are disposed adjacent to each other. In the MR element layout areas
163 and 164, MR elements that are included in the second MR element
row R22 and the third MR element row R23 respectively and provided
with magnetization pinned layers having the same magnetization
direction are disposed adjacent to each other. Note that the
numerical value in each of the MR element layout areas 161 to 164
shows an example of the angle that the magnetization direction of
the magnetization pinned layer of the MR element forms with respect
to the reference direction DR.
In the present embodiment, MR elements with magnetization pinned
layers having the same magnetization direction are disposed
adjacent to each other in each of the MR element layout areas. The
magnetization direction of the magnetization pinned layer in each
MR element may be pinned in the following manner, for example. With
an external magnetic field applied to the unit 40, one MR element
layout area is locally irradiated with a laser beam, whereby the
temperature of the two MR elements in the MR element layout area is
increased and then decreased. According to the present embodiment,
since MR elements with magnetization pinned layers having the same
magnetization direction are disposed adjacent to each other, it is
possible to pin the magnetization direction of the magnetization
pinned layers in two adjacent MR elements simultaneously by
irradiating the two adjacent MR elements with a laser beam
simultaneously. Accordingly, as compared with a case where MR
elements with magnetization pinned layers having different
magnetization directions are disposed adjacent to each other, the
present embodiment allows a reduction in the number of times of
application of the laser beam. This makes it possible to shorten
the time required to fabricate the rotating field sensor.
Here, suppose that MR elements with magnetization pinned layers
having different magnetization directions are disposed adjacent to
each other. In this case, when the MR elements are irradiated with
a laser beam to pin the magnetization directions of the
magnetization pinned layers, other MR elements around the target MR
elements being irradiated could also be subjected to the laser beam
or to the heat resulting from the irradiation of the target MR
elements with the laser beam. As a result, the MR elements around
the target MR elements may become functionally deficient. This
becomes prominent particularly when the laser beam irradiation area
does not have a high resolution. For this reason, if MR elements
with magnetization pinned layers having different magnetization
directions are disposed adjacent to each other, it is necessary
that the adjacent MR elements be spaced apart from each other by
some distance in order to avoid the aforementioned problem. This
results in an increase in size of each of the bridge circuits 14
and 16. In contrast to this, according to the present embodiment,
MR elements with magnetization pinned layers having the same
magnetization direction are disposed adjacent to each other. This
arrangement allows the two adjacent MR elements to be
simultaneously irradiated with a laser beam. Accordingly, the two
adjacent MR elements can be disposed close to each other. The
present embodiment thus allows the bridge circuits 14 and 16 to be
small in size.
The other configuration, operation, and effects of the present
embodiment are the same as those of the first embodiment.
Third Embodiment
A rotating field sensor according to a third embodiment of the
invention will now be described with reference to FIG. 20. FIG. 20
is a circuit diagram showing the configuration of the rotating
field sensor 5 according to the present embodiment. The rotating
field sensor 5 according to the present embodiment has a first
detection circuit 21, a second detection circuit 22, and an
arithmetic circuit 23, instead of the first detection circuit 11,
the second detection circuit 12, and the arithmetic circuit 13 of
the first embodiment. The first detection circuit 21 detects the
intensity of a component of the rotating magnetic field MF in a
first direction D1, and outputs a first signal S1 indicating the
intensity. The second detection circuit 22 detects the intensity of
a component of the rotating magnetic field MF in a second direction
D2, and outputs a second signal S2 indicating the intensity. The
arithmetic circuit 23 calculates, based on the first signal S1 and
the second signal S2, a detected angle value .theta.s having a
correspondence relationship with the angle .theta. that the
direction DM of the rotating magnetic field MF in the reference
position PR forms with respect to the reference direction DR. The
arithmetic circuit 23 calculates the detected angle value .theta.s
by the same method as in the first embodiment. The relationships
between the reference direction DR and the first and second
directions D1 and D2 are the same as the relationships between the
reference direction DR and the first and second directions D1 and
D2 shown in FIG. 2.
The configurations of the first and second detection circuits 21
and 22 will now be described in detail. The first detection circuit
21 has a bridge circuit 24 and a difference detector 25. The bridge
circuit 24 includes a power supply port V3, a ground port G3, two
output ports E31 and E32, first and second MR element rows R31 and
R32 connected in series, and third and fourth MR element rows R33
and R34 connected in series. Each of the first to fourth MR element
rows R31 to R34 is composed of a plurality of MR elements connected
in series. Each of the first to fourth MR element rows R31 to R34
has a first end and a second end.
The first end of the first MR element row R31 and the first end of
the third MR element row R13 are connected to the power supply port
V3. The second end of the first MR element row R31 is connected to
the first end of the second MR element row R32 and the output port
E31. The second end of the third MR element row R33 is connected to
the first end of the fourth MR element row R34 and the output port
E32. The second end of the second MR element row R32 and the second
end of the fourth MR element row R34 are connected to the ground
port G3. A power supply voltage of predetermined magnitude is
applied to the power supply port V3. The ground port G3 is
grounded. The difference detector 25 outputs to the arithmetic
circuit 23 a signal corresponding to the potential difference
between the output ports E31 and E32 as the first signal S1.
In the first detection circuit 21, the magnetization directions of
the magnetization pinned layers in the MR elements are pinned so
that the potential difference between the output ports E31 and E32
varies according to the intensity of the component of the rotating
magnetic field MF in the first direction D1. The first direction D1
therefore serves as a reference direction when the first detection
circuit 21 detects the rotating magnetic field MF. The first
detection circuit 21 detects the intensity of the component of the
rotating magnetic field MF in the first direction D1, and outputs
the first signal S1 indicating the intensity. In the example shown
in FIG. 20, the magnetization directions of the magnetization
pinned layers in the MR elements are pinned so that the potential
difference between the output ports E31 and E32 varies according to
the intensity of the component of the rotating magnetic field MF in
the X direction. In this example, the first direction D1 is the
same as the X direction.
The second detection circuit 22 has a bridge circuit 26 and a
difference detector 27. The bridge circuit 26 includes a power
supply port V4, a ground port G4, two output ports E41 and E42,
first and second MR element rows R41 and R42 connected in series,
and third and fourth MR element rows R43 and R44 connected in
series. Each of the first to fourth MR element rows R41 to R44 is
composed of a plurality of MR elements connected in series. Each of
the first to fourth MR element rows R41 to R44 has a first end and
a second end.
The first end of the first MR element row R41 and the first end of
the third MR element row R43 are connected to the power supply port
V4. The second end of the first MR element row R41 is connected to
the first end of the second MR element row R42 and the output port
E41. The second end of the third MR element row R43 is connected to
the first end of the fourth MR element row R44 and the output port
E42. The second end of the second MR element row R42 and the second
end of the fourth MR element row R44 are connected to the ground
port G4. A power supply voltage of predetermined magnitude is
applied to the power supply port V4. The ground port G4 is
grounded. The difference detector 27 outputs to the arithmetic
circuit 23 a signal corresponding to the potential difference
between the output ports E41 and E42 as the second signal S2.
In the second detection circuit 22, the magnetization directions of
the magnetization pinned layers in the MR elements are pinned so
that the potential difference between the output ports E41 and E42
varies according to the intensity of the component of the rotating
magnetic field MF in the second direction D2. The second direction
D2 therefore serves as a reference direction when the second
detection circuit 22 detects the rotating magnetic field MF. The
second detection circuit 22 detects the intensity of the component
of the rotating magnetic field MF in the second direction D2, and
outputs the second signal S2 indicating the intensity. In the
example shown in FIG. 20, the magnetization directions of the
magnetization pinned layers in the MR elements are pinned so that
the potential difference between the output ports E41 and E42
varies according to the intensity of the component of the rotating
magnetic field MF in the Y direction. In this example, the second
direction D2 is the same as the Y direction.
Now, a detailed description will be given of a plurality of MR
elements that form each MR element row. First, a plurality of MR
elements forming the first to fourth MR element rows R31, R32, R33,
and R34 of the bridge circuit 24 will be described. Each of the
first to fourth MR element rows R31, R32, R33, and R34 is composed
of four MR elements connected in series. The first MR element row
R31 is composed of a first pair of MR elements R311 and R312 and a
second pair of MR elements R313 and R314. The second MR element row
R32 is composed of a first pair of MR elements R321 and R322 and a
second pair of MR elements R323 and R324. The third MR element row
R33 is composed of a first pair of MR elements R331 and R332 and a
second pair of MR elements R333 and R334. The fourth MR element row
R34 is composed of a first pair of MR elements R341 and R342 and a
second pair of MR elements R343 and R344.
One end of the MR element R311 serves as the first end of the first
MR element row R31. The other end of the MR element R311 is
connected to one end of the MR element R312. The other end of the
MR element R312 is connected to one end of the MR element R313. The
other end of the MR element R313 is connected to one end of the MR
element R314. The other end of the MR element R314 serves as the
second end of the first MR element row R31.
One end of the MR element R321 serves as the first end of the
second MR element row R32. The other end of the MR element R321 is
connected to one end of the MR element R322. The other end of the
MR element R322 is connected to one end of the MR element R323. The
other end of the MR element R323 is connected to one end of the MR
element R324. The other end of the MR element R324 serves as the
second end of the second MR element row R32.
One end of the MR element R331 serves as the first end of the third
MR element row R33. The other end of the MR element R331 is
connected to one end of the MR element R332. The other end of the
MR element R332 is connected to one end of the MR element R333. The
other end of the MR element R333 is connected to one end of the MR
element R334. The other end of the MR element R334 serves as the
second end of the third MR element row R33.
One end of the MR element R341 serves as the first end of the
fourth MR element row R34. The other end of the MR element R341 is
connected to one end of the MR element R342. The other end of the
MR element R342 is connected to one end of the MR element R343. The
other end of the MR element R343 is connected to one end of the MR
element R344. The other end of the MR element R344 serves as the
second end of the fourth MR element row R34.
Note that the MR elements R311, R312, R313, and R314 forming the
first MR element row R31 have only to be connected in series
between the first and second ends of the first MR element row R31,
and may be arranged in any order other than that in the example
shown in FIG. 20. Likewise, four MR elements forming each of the
other MR element rows have only to be connected in series between
the first and second ends of the MR element row, and may be
arranged in any order other than that in the example shown in FIG.
20.
Now, a description will be given of the magnetization directions of
the magnetization pinned layers in the MR elements R311 to R314,
R321 to R324, R331 to R334, and R341 to R344. FIG. 21 is an
explanatory diagram showing the magnetization directions of the
magnetization pinned layers in the first pair of MR elements R311
and R312 and the second pair of MR elements R313 and R314 forming
the first MR element row R31. In FIG. 21, the arrows with symbols
D311, D312, D313, and D314 indicate the magnetization directions of
the magnetization pinned layers in the MR elements R111, R112,
R313, and R314, respectively. In FIG. 21, the arrow with symbol D3
indicates the intermediate direction between the magnetization
directions D311 and D312 of the magnetization pinned layers in the
two MR elements R311 and R312 making up the first pair of MR
elements in the first MR element row R31. In FIG. 21, the arrow
with symbol D4 indicates the intermediate direction between the
magnetization directions D313 and D314 of the magnetization pinned
layers in the two MR elements R313 and R314 making up the second
pair of MR elements in the first MR element row R31. Hereinafter,
for the first to fourth MR element rows R31 to R34, the
intermediate direction between the magnetization directions of the
magnetization pinned layers of two MR elements making up the first
pair will be referred to as the third direction, and the
intermediate direction between the magnetization directions of the
magnetization pinned layers of two MR elements making up the second
pair will be referred to as the fourth direction.
As shown in FIG. 21, the magnetization directions D311, D312, D313,
and D314 of the magnetization pinned layers in the MR elements
R311, R312, R313, and R314 are pinned so that the intermediate
direction between the third direction D3 and the fourth direction
D4 is the same as the first direction D1 (the X direction). The
third direction D3 and the fourth direction D4 form a predetermined
relative angle 2.phi. other than 0.degree. and 180.degree.. The
third direction D3 is the direction rotated clockwise from the
first direction D1 by an angle .phi.. The fourth direction D4 is
the direction rotated counterclockwise from the first direction D1
by the angle .phi.. The magnetization directions D311 and D312 of
the magnetization pinned layers in the first pair of MR elements
R311 and R312 form a predetermined relative angle 2.psi. other than
0.degree. and 180.degree.. The magnetization directions D313 and
D314 of the magnetization pinned layers in the second pair of MR
elements R313 and R314 also form a predetermined relative angle
2.psi. other than 0.degree. and 180.degree.. The magnetization
direction D311 of the magnetization pinned layer in the MR element
R311 is the direction rotated clockwise from the third direction D3
by an angle .psi.. The magnetization direction D312 of the
magnetization pinned layer in the MR element R312 is the direction
rotated counterclockwise from the third direction D3 by the angle
.psi.. The magnetization direction D313 of the magnetization pinned
layer in the MR element R313 is the direction rotated clockwise
from the fourth direction D4 by the angle .psi.. The magnetization
direction D314 of the magnetization pinned layer in the MR element
R314 is the direction rotated counterclockwise from the fourth
direction D4 by the angle .psi.. The angles .phi. and .psi. are
different from each other. The angle .phi. is 45.degree., for
example. The angle .psi. is 30.degree., for example.
The magnetization directions of the magnetization pinned layers in
the MR elements R321 to R324 forming the second MR element row R32
are pinned so that the intermediate direction between the third
direction and the fourth direction in the second MR element row R32
is opposite to the first direction D1, i.e., the -X direction. The
magnetization directions of the magnetization pinned layers in the
MR elements R331 to R334 forming the third MR element row R33 are
also pinned so that the intermediate direction between the third
direction and the fourth direction in the third MR element row R33
is opposite to the first direction D1. The magnetization directions
of the magnetization pinned layers in the MR elements R331, R332,
R333, and R334 are the same as those of the magnetization pinned
layers in the MR elements R321, R322, R323, and R324,
respectively.
The magnetization direction of the magnetization pinned layers in
the MR elements R321 and R331 is opposite to the magnetization
direction D311 of the magnetization pinned layer in the MR element
R311 shown in FIG. 21. The magnetization direction of the
magnetization pinned layers in the MR elements R322 and R332 is
opposite to the magnetization direction D312 of the magnetization
pinned layer in the MR element R312 shown in FIG. 21. The
magnetization direction of the magnetization pinned layers in the
MR elements R323 and R333 is opposite to the magnetization
direction D313 of the magnetization pinned layer in the MR element
R313 shown in FIG. 21. The magnetization direction of the
magnetization pinned layers in the MR elements R324 and R334 is
opposite to the magnetization direction D314 of the magnetization
pinned layer in the MR element R314 shown in FIG. 21.
The third direction and the fourth direction in the second MR
element row R32 form a relative angle 2.phi.. The third direction
is the direction rotated clockwise by the angle .phi. from the
direction opposite to the first direction D1. The fourth direction
is the direction rotated counterclockwise by the angle .phi. from
the direction opposite to the first direction D1. The magnetization
directions of the magnetization pinned layers in the MR elements
R321 and R322 form a relative angle 2.psi.. The magnetization
directions of the magnetization pinned layers in the MR elements
R323 and R324 also form the relative angle 2.psi.. The
magnetization direction of the magnetization pinned layer in the MR
element R321 is the direction rotated clockwise from the third
direction by the angle .psi.. The magnetization direction of the
magnetization pinned layer in the MR element R322 is the direction
rotated counterclockwise from the third direction by the angle
.psi.. The magnetization direction of the magnetization pinned
layer in the MR element R323 is the direction rotated clockwise
from the fourth direction by the angle .psi.. The magnetization
direction of the magnetization pinned layer in the MR element R324
is the direction rotated counterclockwise from the fourth direction
by the angle .psi..
The third direction and the fourth direction in the third MR
element row R33 are the same as the third direction and the fourth
direction in the second MR element row R32, respectively. The
magnetization directions of the magnetization pinned layers in the
MR elements R331 and R332 form a relative angle 2.psi.. The
magnetization directions of the magnetization pinned layers in the
MR elements R333 and R334 also form the relative angle 2.psi.. The
magnetization direction of the magnetization pinned layer in the MR
element R331 is the direction rotated clockwise from the third
direction by the angle .psi.. The magnetization direction of the
magnetization pinned layer in the MR element R332 is the direction
rotated counterclockwise from the third direction by the angle
.psi.. The magnetization direction of the magnetization pinned
layer in the MR element R333 is the direction rotated clockwise
from the fourth direction by the angle .psi.. The magnetization
direction of the magnetization pinned layer in the MR element R334
is the direction rotated counterclockwise from the fourth direction
by the angle .psi..
The magnetization directions of the magnetization pinned layers in
the MR elements R341 to R344 forming the fourth MR element row R34
are pinned so that the intermediate direction between the third
direction and the fourth direction in the fourth MR element row R34
is the same as the first direction D1 (the X direction). The
magnetization directions of the magnetization pinned layers in the
MR elements R341, R342, R343, and R344 are the same as those of the
magnetization pinned layers in the MR elements R311, R312, R313,
and R314, respectively.
The third direction and the fourth direction in the fourth MR
element row R34 are the same as the third direction and the fourth
direction in the first MR element row R31, respectively. The
magnetization directions of the magnetization pinned layers in the
MR elements R341 and R342 form a relative angle 2.psi.. The
magnetization directions of the magnetization pinned layers in the
MR elements R343 and R344 also form the relative angle 2.psi.. The
magnetization direction of the magnetization pinned layer in the MR
element R341 is the direction rotated clockwise from the third
direction by the angle .psi.. The magnetization direction of the
magnetization pinned layer in the MR element R342 is the direction
rotated counterclockwise from the third direction by the angle
.psi.. The magnetization direction of the magnetization pinned
layer in the MR element R343 is the direction rotated clockwise
from the fourth direction by the angle .psi.. The magnetization
direction of the magnetization pinned layer in the MR element R344
is the direction rotated counterclockwise from the fourth direction
by the angle .psi..
Now, a description will be given of MR elements that form the first
to fourth MR element rows R41, R42, R43, and R44 of the bridge
circuit 26. Each of the first to fourth MR element rows R41, R42,
R43, and R44 is composed of four MR elements connected in series.
The first MR element row R41 is composed of a third pair of MR
elements R411 and R412 and a fourth pair of MR elements R413 and
R414. The second MR element row R42 is composed of a third pair of
MR elements R421 and R422 and a fourth pair of MR elements R423 and
R424. The third MR element row R43 is composed of a third pair of
MR elements R431 and R432 and a fourth pair of MR elements R433 and
R434. The fourth MR element row R44 is composed of a third pair of
MR elements R441 and R442 and a fourth pair of MR elements R443 and
R444.
One end of the MR element R411 serves as the first end of the first
MR element row R41. The other end of the MR element R411 is
connected to one end of the MR element R412. The other end of the
MR element R412 is connected to one end of the MR element R413. The
other end of the MR element R413 is connected to one end of the MR
element R414. The other end of the MR element R414 serves as the
second end of the first MR element row R41.
One end of the MR element R421 serves as the first end of the
second MR element row R42. The other end of the MR element R421 is
connected to one end of the MR element R422. The other end of the
MR element R422 is connected to one end of the MR element R423. The
other end of the MR element R423 is connected to one end of the MR
element R424. The other end of the MR element R424 serves as the
second end of the second MR element row R42.
One end of the MR element R431 serves as the first end of the third
MR element row R43. The other end of the MR element R431 is
connected to one end of the MR element R432. The other end of the
MR element R432 is connected to one end of the MR element R433. The
other end of the MR element R433 is connected to one end of the MR
element R434. The other end of the MR element R434 serves as the
second end of the third MR element row R43.
One end of the MR element R441 serves as the first end of the
fourth MR element row R44. The other end of the MR element R441 is
connected to one end of the MR element R442. The other end of the
MR element R442 is connected to one end of the MR element R443. The
other end of the MR element R443 is connected to one end of the MR
element R444. The other end of the MR element R444 serves as the
second end of the fourth MR element row R44.
Note that the MR elements R411, R412, R413, and R414 forming the
first MR element row R41 have only to be connected in series
between the first and second ends of the first MR element row R41,
and may be arranged in any order other than that in the example
shown in FIG. 20. Likewise, four MR elements forming each of the
other MR element rows have only to be connected in series between
the first and second ends of the MR element row, and may be
arranged in any order other than that in the example shown in FIG.
20.
Now, a description will be given of the magnetization directions of
the magnetization pinned layers in the MR elements R411 to R414,
R421 to R424, R431 to R434, and R441 to R444. For the first to
fourth MR element rows R41 to R44, the intermediate direction
between the magnetization directions of the magnetization pinned
layers of two MR elements making up the third pair will be referred
to as the fifth direction, and the intermediate direction between
the magnetization directions of the magnetization pinned layers of
two MR elements making up the fourth pair will be referred to as
the sixth direction. The magnetization directions of the
magnetization pinned layers in the MR elements R411 to R414 forming
the first MR element row R41 are pinned so that the intermediate
direction between the fifth direction and the sixth direction in
the first MR element row R41 is the same as the second direction D2
(the Y direction). The magnetization directions of the
magnetization pinned layers in the MR elements R441 to R444 forming
the fourth MR element row R44 are also pinned so that the
intermediate direction between the fifth direction and the sixth
direction in the fourth MR element row R44 is the same as the
second direction D2. The magnetization directions of the
magnetization pinned layers in the MR elements R441, R442, R443,
and R444 are the same as those of the magnetization pinned layers
in the MR elements R411, R412, R413, and R414, respectively.
The magnetization direction of the magnetization pinned layers in
the MR elements R411 and R441 is the direction rotated
counterclockwise by 90.degree. from the magnetization direction
D314 of the magnetization pinned layer in the MR element R314 shown
in FIG. 21. The magnetization direction of the magnetization pinned
layers in the MR elements R412 and R442 is the direction rotated
counterclockwise by 90.degree. from the magnetization direction
D313 of the magnetization pinned layer in the MR element R313 shown
in FIG. 21. The magnetization direction of the magnetization pinned
layers in the MR elements R413 and R443 is the direction rotated
counterclockwise by 90.degree. from the magnetization direction
D312 of the magnetization pinned layer in the MR element R312 shown
in FIG. 21. The magnetization direction of the magnetization pinned
layers in the MR elements R414 and R444 is the direction rotated
counterclockwise by 90.degree. from the magnetization direction
D311 of the magnetization pinned layer in the MR element R311 shown
in FIG. 21.
The fifth direction and the sixth direction in the first MR element
row R41 form a relative angle 2.phi.. The fifth direction is the
direction rotated counterclockwise from the second direction D2 by
the angle .phi.. The sixth direction is the direction rotated
clockwise from the second direction D2 by the angle .phi.. The
magnetization directions of the magnetization pinned layers in the
MR elements R411 and R412 form a relative angle 2.psi.. The
magnetization directions of the magnetization pinned layers in the
MR elements R413 and R414 also form the relative angle 2.psi.. The
magnetization direction of the magnetization pinned layer in the MR
element R411 is the direction rotated counterclockwise from the
fifth direction by the angle .psi.. The magnetization direction of
the magnetization pinned layer in the MR element R412 is the
direction rotated clockwise from the fifth direction by the angle
.psi.. The magnetization direction of the magnetization pinned
layer in the MR element R413 is the direction rotated
counterclockwise from the sixth direction by the angle .psi.. The
magnetization direction of the magnetization pinned layer in the MR
element R414 is the direction rotated clockwise from the sixth
direction by the angle .psi..
The fifth direction and the sixth direction in the fourth MR
element row R44 are the same as the fifth direction and the sixth
direction in the first MR element row R41, respectively. The
magnetization directions of the magnetization pinned layers in the
MR elements 11441 and R442 form a relative angle 2.psi.. The
magnetization directions of the magnetization pinned layers in the
MR elements 11443 and R444 also form the relative angle 2.psi.. The
magnetization direction of the magnetization pinned layer in the MR
element R441 is the direction rotated counterclockwise from the
fifth direction by the angle .psi.. The magnetization direction of
the magnetization pinned layer in the MR element R442 is the
direction rotated clockwise from the fifth direction by the angle
.psi.. The magnetization direction of the magnetization pinned
layer in the MR element R443 is the direction rotated
counterclockwise from the sixth direction by the angle .psi.. The
magnetization direction of the magnetization pinned layer in the MR
element R444 is the direction rotated clockwise from the sixth
direction by the angle .psi..
The magnetization directions of the magnetization pinned layers in
the MR elements R421 to R424 forming the second MR element row R42
are pinned so that the intermediate direction between the fifth
direction and the sixth direction in the second MR element row R42
is opposite to the second direction D2, i.e., the -Y direction. The
magnetization directions of the magnetization pinned layers in the
MR elements R431 to R434 forming the third MR element row R43 are
also pinned so that the intermediate direction between the fifth
direction and the sixth direction in the third MR element row R43
is opposite to the second direction D2. The magnetization
directions of the magnetization pinned layers in the MR elements
R431, R432, R433, and R434 are the same as those of the
magnetization pinned layers in the MR elements R421, R422, R423,
and R424, respectively.
The magnetization direction of the magnetization pinned layers in
the MR elements R421 and R431 is opposite to the magnetization
direction of the magnetization pinned layers in the MR elements
R414 and R444. The magnetization direction of the magnetization
pinned layers in the MR elements R422 and R432 is opposite to the
magnetization direction of the magnetization pinned layers in the
MR elements R413 and R443. The magnetization direction of the
magnetization pinned layers in the MR elements R423 and R433 is
opposite to the magnetization direction of the magnetization pinned
layers in the MR elements R412 and R442. The magnetization
direction of the magnetization pinned layers in the MR elements
R424 and R434 is opposite to the magnetization direction of the
magnetization pinned layers in the MR elements R411 and R441.
The fifth direction and the sixth direction in the second MR
element row R42 form a relative angle 2.phi.. The fifth direction
is the direction rotated clockwise by the angle .phi. from the
direction opposite to the second direction D2. The sixth direction
is the direction rotated counterclockwise by the angle .phi. from
the direction opposite to the second direction D2. The
magnetization directions of the magnetization pinned layers in the
MR elements R421 and R422 form a relative angle 2.psi.. The
magnetization directions of the magnetization pinned layers in the
MR elements R423 and R424 also form the relative angle 2.psi.. The
magnetization direction of the magnetization pinned layer in the MR
element R421 is the direction rotated clockwise from the fifth
direction by the angle .psi.. The magnetization direction of the
magnetization pinned layer in the MR element R422 is the direction
rotated counterclockwise from the fifth direction by the angle
.psi.. The magnetization direction of the magnetization pinned
layer in the MR element R423 is the direction rotated clockwise
from the sixth direction by the angle .psi.. The magnetization
direction of the magnetization pinned layer in the MR element R424
is the direction rotated counterclockwise from the sixth direction
by the angle .psi..
The fifth direction and the sixth direction in the third MR element
row R43 are the same as the fifth direction and the sixth direction
in the second MR element row R42, respectively. The magnetization
directions of the magnetization pinned layers in the MR elements
R431 and R432 form a relative angle 2.psi.. The magnetization
directions of the magnetization pinned layers in the MR elements
R433 and R434 also form the relative angle 2.psi.. The
magnetization direction of the magnetization pinned layer in the MR
element R431 is the direction rotated clockwise from the fifth
direction by the angle .psi.. The magnetization direction of the
magnetization pinned layer in the MR element R432 is the direction
rotated counterclockwise from the fifth direction by the angle
.psi.. The magnetization direction of the magnetization pinned
layer in the MR element R433 is the direction rotated clockwise
from the sixth direction by the angle .psi.. The magnetization
direction of the magnetization pinned layer in the MR element R434
is the direction rotated counterclockwise from the sixth direction
by the angle .psi..
As has been described, each MR element row in the first and the
second detection circuits 21 and 22 is composed of a plurality of
MR elements each having a magnetization pinned layer whose
magnetization direction is pinned in a predetermined direction.
None of the first to fourth MR element rows R31, R32, R33, and R34
in the first detection circuit 21 includes any MR element that has
a magnetization pinned layer whose magnetization direction is
pinned in the first direction D1 (the X direction) or in the
direction opposite to the first direction D1 (the -X direction).
None of the first to fourth MR element rows R41, R42, R43, and R44
in the second detection circuit 22 includes any MR element that has
a magnetization pinned layer whose magnetization direction is
pinned in the second direction D2 (the Y direction) or in the
direction opposite to the second direction D2 (the -Y
direction).
Now, a description will be given of a specific example of
magnetization directions of the magnetization pinned layers of MR
elements. First, the following description will deal with a
plurality of MR elements forming each MR element row in the first
detection circuit 21. The magnetization direction of the
magnetization pinned layer of each MR element can be expressed
using the angle that the magnetization direction forms with respect
to the reference direction DR. Likewise, the third direction and
the fourth direction in the first to fourth MR element rows R31 to
R34 can also be expressed using the angles that the third direction
and the fourth direction form with respect to the reference
direction DR. Here, the angle that the intermediate direction
between the third and fourth directions forms with respect to the
reference direction DR will be referred to as the angle of the
first type. The angle that the third or fourth direction forms with
respect to the reference direction DR will be referred to as the
angle of the second type. The angle that the magnetization
direction of the magnetization pinned layer of each MR element
included in the first detection circuit 21 forms with respect to
the reference direction DR will be referred to as the angle of the
third type. The angle .phi. shown in FIG. 21 shall be 45.degree.,
and the angle .psi. shown in FIG. 21 shall be 30.degree..
FIG. 22 is an explanatory diagram illustrating the relationship
between the angles of the first to third types in the first
detection circuit 21. In FIG. 22, each numerical value in the box
denoted by reference numeral 101 indicates the angle of the first
type, each numerical value in the box denoted by reference numeral
102 indicates the angle of the second type, and each numerical
value in the box denoted by reference numeral 103 indicates the
angle of the third type. In the present embodiment, the first
direction D1 is the direction rotated by 90.degree. from the
reference direction DR. Accordingly, the angle of the first type
takes on 90.degree. and 270.degree.. The angle of the second type
corresponding to the angle 90.degree. of the first type is
45.degree. and 135.degree.. The angle of the second type
corresponding to the angle 270.degree. of the first type is
225.degree. and 315.degree.. The angle of the third type
corresponding to the angle 45.degree. of the second type is
15.degree. and 75.degree.. The angle of the third type
corresponding to the angle 135.degree. of the second type is
105.degree. and 165.degree.. The angle of the third type
corresponding to the angle 225.degree. of the second type is
195.degree. and 255.degree.. The angle of the third type
corresponding to the angle 315.degree. of the second type is
285.degree. and 345.degree..
The ideal component of the resistance of a pair of MR elements that
have magnetization pinned layers whose magnetization directions are
15.degree. and 75.degree. has the same phase as that of the ideal
component of the resistance of a virtual MR element that has a
magnetization pinned layer whose magnetization direction is
intermediate between 15.degree. and 75.degree., i.e., 45.degree..
The same holds true for the ideal component of the resistance of
other pairs of MR elements. Furthermore, the ideal component of the
resistance of each of the MR element rows R31 and R34 composed of
four MR elements that have magnetization pinned layers whose
magnetization directions are 15.degree., 75.degree., 105.degree.,
and 165.degree. has the same phase as that of the ideal component
of the resistance of a virtual MR element that has a magnetization
pinned layer whose magnetization direction is 90.degree.. Likewise,
the ideal component of the resistance of each of the MR element
rows R32 and R33 composed of four MR elements that have
magnetization pinned layers whose magnetization directions are
195.degree., 255.degree., 285.degree., and 345.degree. has the same
phase as that of the ideal component of the resistance of a virtual
MR element that has a magnetization pinned layer whose
magnetization direction is 270.degree.. Consequently, according to
the present embodiment, the first detection circuit 21 is able to
detect the intensity of the component of the rotating magnetic
field MF in the first direction D1 and to output the first signal
S1 indicating the intensity even if the first detection circuit 21
does not include any MR element that has a magnetization pinned
layer whose magnetization direction is pinned in the first
direction D1 or in the direction opposite to the first direction
D1.
Next, the following description will deal with a plurality of MR
elements forming each MR element row in the second detection
circuit 22. Like the third and fourth directions, the fifth
direction and the sixth direction in the first to fourth MR element
rows R41 to R44 can be expressed using the angles that the fifth
direction and the sixth direction form with respect to the
reference direction DR. Here, as with the third and fourth
directions, the angle that the intermediate direction between the
fifth and sixth directions forms with respect to the reference
direction DR will be referred to as the angle of the first type,
and the angle that the fifth or sixth direction forms with respect
to the reference direction DR will be referred to as the angle of
the second type. Furthermore, the angle that the magnetization
direction of the magnetization pinned layer of each MR element
included in the second detection circuit 22 forms with respect to
the reference direction DR will be referred to as the angle of the
third type.
FIG. 23 is an explanatory diagram illustrating the relationship
between the angles of the first to third types in the second
detection circuit 22. In FIG. 23, each numerical value in the box
denoted by reference numeral 111 indicates the angle of the first
type, each numerical value in the box denoted by reference numeral
112 indicates the angle of the second type, and each numerical
value in the box denoted by reference numeral 113 indicates the
angle of the third type. In the present embodiment, the second
direction D2 coincides with the reference direction DR.
Accordingly, the angle of the first type takes on 0.degree. and
180.degree.. The angle of the second type corresponding to the
angle 0.degree. of the first type is 45.degree. and 315.degree..
The angle of the second type corresponding to the angle 180.degree.
of the first type is 135.degree. and 225.degree.. The angle of the
third type corresponding to the angle 45.degree. of the second type
is 15.degree. and 75.degree.. The angle of the third type
corresponding to the angle 315.degree. of the second type is
285.degree. and 345.degree.. The angle of the third type
corresponding to the angle 135.degree. of the second type is
105.degree. and 165.degree.. The angle of the third type
corresponding to the angle 225.degree. of the second type is
195.degree. and 255.degree..
Like the first detection circuit 21, the second detection circuit
22 is able to detect the intensity of the component of the rotating
magnetic field MF in the second direction D2 and to output the
second signal S2 indicating the intensity even if the second
detection circuit 22 does not include any MR element that has a
magnetization pinned layer whose magnetization direction is pinned
in the second direction D2 or in the direction opposite to the
second direction D2.
The arrangement of a plurality of MR elements in the present
embodiment will now be described. Like the second embodiment, the
present embodiment is configured so that MR elements that are
included in two different MR element rows and provided with
magnetization pinned layers having the same magnetization direction
are disposed adjacent to each other. More specifically, in the
first detection circuit 21, MR elements that are included in the
first MR element row R31 and the fourth MR element row R34
respectively and provided with magnetization pinned layers having
the same magnetization direction are disposed adjacent to each
other, while MR elements that are included in the second MR element
row R32 and the third MR element row R33 respectively and provided
with magnetization pinned layers having the same magnetization
direction are disposed adjacent to each other. In the second
detection circuit 22, MR elements that are included in the first MR
element row R41 and the fourth MR element row R44 respectively and
provided with magnetization pinned layers having the same
magnetization direction are disposed adjacent to each other, while
MR elements that are included in the second MR element row R42 and
the third MR element row R43 respectively and provided with
magnetization pinned layers having the same magnetization direction
are disposed adjacent to each other.
FIG. 24 is a plan view of a unit 80 that incorporates the bridge
circuits 24 and 26 shown in FIG. 20. The unit 80 includes a
substrate 81, with the bridge circuits 24 and 26 provided thereon.
The bridge circuit 24 is located on the lower side in FIG. 24. The
bridge circuit 26 is located on the upper side in FIG. 24. The
plurality of ports of the bridge circuits 24 and 26 are arranged on
the substrate 81, near peripheral edges of the substrate 81.
The bridge circuit 24 has eight MR element layout areas 241, 242,
243, 244, 245, 246, 247, and 248. Two MR elements are located in
each of the MR elements layout areas 241 to 248. In the MR element
layout areas 241 to 244, MR elements that are included in the first
MR element row R31 and the fourth MR element row R34 respectively
and provided with magnetization pinned layers having the same
magnetization direction are disposed adjacent to each other. In the
MR element layout areas 245 to 248, MR elements that are included
in the second MR element row R32 and the third MR element row R33
respectively and provided with magnetization pinned layers having
the same magnetization direction are disposed adjacent to each
other. Note that the numerical value in each of the MR element
layout areas 241 to 248 indicates an example of the angle of the
third type shown in FIG. 22, that is, the angle that the
magnetization direction of the magnetization pinned layer of the MR
element forms with respect to the reference direction DR.
The bridge circuit 26 has eight MR element layout areas 261, 262,
263, 264, 265, 266, 267, and 268. Two MR elements are located in
each of the MR elements layout areas 261 to 268. In the MR element
layout areas 261 to 264, MR elements that are included in the first
MR element row R41 and the fourth MR element row R44 respectively
and provided with magnetization pinned layers having the same
magnetization direction are disposed adjacent to each other. In the
MR element layout areas 265 to 268, MR elements that are included
in the second MR element row R42 and the third MR element row R43
respectively and provided with magnetization pinned layers having
the same magnetization direction are disposed adjacent to each
other. Note that the numerical value in each of the MR element
layout areas 261 to 268 indicates an example of the angle of the
third type shown in FIG. 23, that is, the angle that the
magnetization direction of the magnetization pinned layer of the MR
element forms with respect to the reference direction DR.
In the present embodiment, as in the second embodiment, the
magnetization direction of the magnetization pinned layer in each
MR element may be pinned in the following manner, for example. With
an external magnetic field applied to the unit 80, one MR element
layout area is locally irradiated with a laser beam, whereby the
temperature of the two MR elements in the MR element layout area is
increased and then decreased.
The operation and effects of the rotating field sensor 5 will now
be described with reference to FIG. 25 to FIG. 33. The following
description is made taking the second MR element row R32 of the
first detection circuit 21 as an example, with comparison made with
virtual MR elements and a virtual MR element row. First, the
virtual MR element row and first to third virtual MR elements will
be described. The first virtual MR element is configured so that
the magnetization pinned layers in the four MR elements R321, R322,
R323, and R324 forming the second MR element row R32 have the same
magnetization direction. The second virtual MR element is
configured so that the magnetization pinned layers in the second
pair of MR elements R323 and R324 have the same magnetization
direction. The third virtual MR element is configured so that the
magnetization pinned layers in the first pair of MR elements R321
and R322 have the same magnetization direction.
The virtual MR element row is composed of the second and third
virtual MR elements connected in series. The virtual MR element row
has a first end and a second end, as does the second MR element row
R32. One end of the second virtual MR element serves as the first
end of the virtual MR element row. The other end of the second
virtual MR element is connected to one end of the third virtual MR
element. The other end of the third virtual MR element serves as
the second end of the virtual MR element row.
The magnetization direction of the magnetization pinned layer in
the first virtual MR element is opposite to the first direction D1.
The intermediate direction between the magnetization directions of
the magnetization pinned layers in the second and third virtual MR
elements is also opposite to the first direction D1. The
magnetization direction of the magnetization pinned layer in the
second virtual MR element is the direction rotated counterclockwise
by 45.degree. from the direction opposite to the first direction
D1. The magnetization direction of the magnetization pinned layer
in the third virtual MR element is the direction rotated clockwise
by 45.degree. from the direction opposite to the first direction
D1.
Each of FIG. 25 to FIG. 33 shows the waveform of the periodically
varying component of the potential difference across an MR element
or the potential difference between the first and second ends of
the MR element row. In FIG. 25 to FIG. 33, the horizontal axis
represents the angle .theta., while the vertical axis represents
the normalized output. The normalized output on the vertical axis
indicates the values of the potential difference where the maximum
value of the periodically varying component of the potential
difference between the first and second ends of the second MR
element row R32 shown in FIG. 33 is assumed as 1. The waveforms
shown in FIG. 25 to FIG. 33 were generated by simulation.
FIG. 25 is a waveform chart showing the waveform of the
periodically varying component of the potential difference across
the first virtual MR element. Reference numeral 300 indicates the
waveform of the periodically varying component of the potential
difference. Reference numeral 301 indicates an ideal sinusoidal
curve. Reference numeral 302 indicates the waveform of the second
potential difference harmonic component that results from the
second harmonic component included in the resistance harmonic
component of the MR element. Reference numeral 303 indicates the
waveform of the third potential difference harmonic component that
results from the third harmonic component included in the
resistance harmonic component of the MR element. As shown in FIG.
25, the waveform of the periodically varying component of the
potential difference shown by reference numeral 300 is distorted
from the sinusoidal curve because it includes the second and third
potential difference harmonic components.
FIG. 26 shows the waveform of the periodically varying component of
the potential difference across the second virtual MR element. FIG.
27 shows the waveform of the periodically varying component of the
potential difference across the third virtual MR element. Reference
numerals 310 and 320 in FIG. 26 and FIG. 27 indicate the waveforms
of the periodically varying components of the respective potential
differences. Reference numerals 311 and 321 each indicate an ideal
sinusoidal curve. Reference numerals 312 and 322 indicate the
waveforms of the second potential difference harmonic components
that result from the second harmonic components included in the
respective resistance harmonic components of the MR elements.
Reference numerals 313 and 323 indicate the waveforms of the third
potential difference harmonic components that result from the third
harmonic components included in the respective resistance harmonic
components of the MR elements. The waveforms shown in FIG. 26
differ from the waveforms shown in FIG. 25 in phase by .pi./4
(45.degree.). The waveforms shown in FIG. 27 differ from the
waveforms shown in FIG. 25 in phase by -.pi./4 (-45.degree.).
FIG. 28 shows the waveform (reference numeral 330) of the
periodically varying component of the potential difference between
the first end and the second end of the virtual MR element row.
FIG. 28 also shows the waveforms (reference numerals 310 and 320)
of the periodically varying components of the potential differences
shown in FIG. 27 and FIG. 28. As shown in FIG. 26 and FIG. 27, the
second potential difference harmonic components denoted by
reference numerals 312 and 322 have opposite phases. Consequently,
those second potential difference harmonic components cancel each
other out in the virtual MR element row. However, the third
potential difference harmonic components denoted by reference
numerals 313 and 323 cannot cancel each other out in the virtual MR
element row. Accordingly, the waveform of the periodically varying
component of the potential difference denoted by reference numeral
320 is distorted from the sinusoidal curve.
FIG. 29 shows the waveform of the periodically varying component of
the potential difference across the MR element R323. FIG. 30 shows
the waveform of the periodically varying component of the potential
difference across the MR element R324. FIG. 31 shows the waveform
of the periodically varying component of the potential difference
across the MR element R322. FIG. 32 shows the waveform of the
periodically varying component of the potential difference across
the MR element R321. The waveforms shown in FIG. 29 to FIG. 32 are
obtained with the angles .phi. and .psi. of FIG. 21 set to
45.degree. and 30.degree., respectively. Reference numerals 340,
350, 360, and 370 in FIG. 29 to FIG. 32 indicate the waveforms of
the periodically varying components of the respective potential
differences. Reference numerals 341, 351, 361 and 371 each indicate
an ideal sinusoidal curve. Reference numerals 342, 352, 362, and
372 indicate the waveforms of the second potential difference
harmonic components that result from the second harmonic components
included in the respective resistance harmonic components of the MR
elements. Reference numerals 343, 353, 363, and 373 indicate the
waveforms of the third potential difference harmonic components
that result from the third harmonic components included in the
respective resistance harmonic components of the MR elements.
The waveforms shown in FIG. 29 differ from the waveforms shown in
FIG. 25 in phase by .pi./12 (15.degree.), and differ from the
waveforms shown in FIG. 26 in phase by -.pi./6 (-30.degree.). The
waveforms shown in FIG. 30 differ from the waveforms shown in FIG.
25 in phase by 5.pi./12 (75.degree.), and differ from the waveforms
shown in FIG. 26 in phase by .pi./6 (30.degree.). The waveforms
shown in FIG. 31 differ from the waveforms shown in FIG. 25 in
phase by -.pi./12 (-15.degree.), and differ from the waveforms
shown in FIG. 27 in phase by .pi./6 (30.degree.). The waveforms
shown in FIG. 32 differ from the waveforms shown in FIG. 25 in
phase by -5.pi./12 (-75.degree.), and differ from the waveforms
shown in FIG. 27 in phase by .pi./6 (30.degree.).
FIG. 33 shows the waveform (reference numeral 380) of the
periodically varying component of the potential difference between
the first end and the second end of the second MR element row R32.
As with FIG. 29 to FIG. 32, the waveform shown in FIG. 33 is
obtained with the angles .phi. and .psi. of FIG. 21 set to
45.degree. and 30.degree., respectively. FIG. 33 also shows the
waveforms (reference numerals 340, 350, 360, and 370) of the
periodically varying components of the respective potential
differences shown in FIG. 29 to FIG. 32. As shown in FIG. 29 and
FIG. 32, the phases of the second potential difference harmonic
components denoted by reference numerals 342 and 372 are different
from each other by 2.phi. (90.degree.), and are thus opposite to
each other. As shown in FIG. 30 and FIG. 31, the phases of the
second potential difference harmonic components denoted by
reference numerals 352 and 362 are different from each other by
2.phi. (90.degree.), and are thus opposite to each other. As shown
in FIG. 29 and FIG. 30, the phases of the third potential
difference harmonic components denoted by reference numerals 343
and 353 are different from each other by 2.psi. (60.degree.), and
are thus opposite to each other. As shown in FIG. 31 and FIG. 32,
the phases of the third potential difference harmonic components
denoted by reference numerals 363 and 373 are different from each
other by 2.psi. (60.degree.), and are thus opposite to each other.
Consequently, in the second MR element row R32, the second and
third potential difference harmonic components in the four MR
elements forming the MR element row are canceled out. As a result,
the periodically varying component of the potential difference
denoted by reference numeral 380 has a sinusoidal waveform with
reduced distortion, i.e., with a reduced potential difference
harmonic component, as compared with the waveform denoted by
reference numeral 300 in FIG. 25 and the waveform denoted by
reference numeral 330 in FIG. 28. According to the present
embodiment, it is thus possible to reduce two different-order
(second and third) potential difference harmonic components in the
second MR element row R32. This holds true for the other MR element
rows.
According to the present embodiment, setting .phi. to 45.degree.
and .psi. to 30.degree. allows reducing the second and third
potential difference harmonic components in each MR element row.
This makes it possible to reduce the error resulting from the
second and third potential difference harmonic components in the
angle detected by the rotating field sensor 5.
The above description has dealt with an example where the second
and third potential difference harmonic components are reduced in
each MR element row by setting .phi. and .psi. to 45.degree. and
30.degree., respectively. According to the present embodiment,
however, it is also possible to reduce potential difference
harmonic components of any two different orders in each MR element
row by setting .phi. or .psi. to 1/4 the period of the potential
difference harmonic component that is desired to reduce.
The other configuration, operation, and effects of the present
embodiment are the same as those of the second embodiment.
The present invention is not limited to the foregoing embodiments,
and various modifications may be made thereto. For example, each MR
element row may include four or more pairs of MR elements so that
potential difference harmonic components of three or more orders
can be reduced in each MR element row. For example, each MR element
in the third embodiment may be replaced with two MR elements having
magnetization pinned layers whose magnetization directions are
different by -22.5.degree. and 22.5.degree. from the magnetization
direction of the magnetization pinned layer in a corresponding MR
element in the third embodiment. This makes it possible to reduce
the error resulting from the second, third, and fourth potential
difference harmonic components in the angle detected by the
rotating field sensor.
It is apparent that the present invention can be carried out in
various forms and modifications in the light of the foregoing
descriptions. Accordingly, within the scope of the following claims
and equivalents thereof, the present invention can be carried out
in forms other than the foregoing most preferable embodiments.
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